Hi everyone, in desperate need of help

Hello, my name is Will. I just bought my first bike last weekend. I picked up a 1982 Yamaha Seca 750. Just the other day i went to go start it up and it was back firing on me. The guy i bought the bike off of said that the carbs were done not too long ago, and i replaced 3 out of the 4 spark plugs and the last one didn't look too bad. Now it only back fires when the choke is off. If the choke is on there's no back fire whatsoever. If anyone has a clue on what it could be that would be great. I dont have much money to put into it.

 

too much fuel. carb problem. you made need to adjust the pilot screws on your carbs. Im sure a real pro will be by soon to lend a good word.

 

You are going to have to do some work getting the Bike tuned-up right.

You have an obvious Fuel Delivery issue that might need a Carb Cleaning and a Sync and Set to get right.

Wou going to do the work or do you have to farm it out?

 

here is one of the standard questions...

where are you at?

it does sound as though the mixture isnt right but i would think that if backfires with the choke off, it should REALLY run bad with the choke on. (enriching the mixture puts more gas into it)...

heck i dont know, i had MiCarl fix my bike in 20 minutes something i couldnt do in 5 weeks...

d

 

Sorry to disagree with some of your replies.

Backfiring IMO, is normally the result of a weak mixture.

If the choke is OFF (ie, the choke is not doing anything) & it is backfiring, you have a weak mixture

If the choke is ON or partially ON (ie, engaged or partially engaged) & it runs OK, that is telling you that the mixture is set too weak & needs the enrichment of the choke to get the engine to run reasonably OK.

You do not have too much fuel, but not enough. The choke provides the richer mixture to allow it to run properly.

 

Pulling and cleaning the carbs will be necessary, no ifs ands or buts about it.

 

We're about at the point where it is valid to say that if you haven't had your Carbs Cleaned in a long time ... or, you don't know if they were ever done ... you are due for a Carb Cleaning just as preventative maintenance.

If you have trouble Idling or you don't have the power in off-idle performance ... Mid-range and Wide-open Throttle ... you need a Carb Cleaning.

Any Bike just bought that has been sitting around for more than a few months is prime candidate for needing a Carb Cleaning.

It's a necessary step in maintaining the good health of the engine.

 

check your valve tolerances too they can cause backfiring!

 

Well im in new hampshire in the manchester area and i'd have to find someone to do the work for me i know nothing about bikes or carbs. I do have a repair manual on the bike but im not sure if carb work is something someone with no experience can do. Thanks for all the input.

 

go get yourself some experience. i didnt know anything when i got my bike but between a Clymer manual and a lot of time and a few beers i can have the carbs off, cleaned and back on in no time at all. it all comes with practice.

 

You are just a 45-Minute ride from my place.

I'll help you get tuned-up ... and I won't charge you and arm and a leg either.

Give me PM and we'll set something up for a weekend or a weekday when you can sneak by.

 

The carbs are quite simple, mechanically speaking.

The process of making DARNED SURE that you get them unbelievably, positively zestfully clean is a matter of stick-to-it-ness and resisting all attempts to take "shortcuts" or to brush off the tedious aspects of it. Many of the passages in these carbs are tiny, and it's that "tiny-ness" that bites most people, as they don't want to or don't realize the amount of effort that has to be undertaken to deal with such small passages.

If you read through these forums, you'll see many tales of woe of people who are now "cleaning" their carbs for the 2nd, 3rd, or 4th time BEFORE they get it right. The problem is, they never really "cleaned" them correctly the first, 2nd, and 3rd time. After all of the frustration and hassle involved, by the time they get around to the 4th go-around, then they understand that when people who have SUCCESSFULLY rebuilt carbs say things like "you'd better make SURE that you get clear flow through each and every passage, and you'd better polish that piston diaphram bore", etc. aren't just saying that to be over-the-top retentive about their own habits and style of working on these carbs, what they're really doing is issuing an experienced WARNING: do it right, or keep doing it again, and again, and again. And although they're kind of fun little critters to play with, taking them all apart and putting Humpty Carby all back together again, well, it's time better spent on other things.

One last note: "cleaning" the carbs (internally, not just making them look pretty on the outside) is just one of the small subsets of tasks necessary to the proper REBUILDING of the carbs. I cannot stress this point enough. The use of the term "cleaning" is used as if it were the end goal of the process; in reality, the proper way to think about it would be this:

"A complete and exceptiional level of carb CLEANING is a vital and necessary part of the process of properly REBUILDING the carbs."

And what are the other components of the rebuilding puzzle?

a) replacing the worn, missing, or necessary "wear parts" on the carb.

These would be the idle mixture o-rings, washers, and maybe even the springs.

The carb bowl gaskets.

The carb throttle shaft seals.

The float valve needles and seats.

Any incorrectly sized or damaged jets.

Inspection of the piston rubber disphram for any holes, thin spots, etc.


b) Proper "service" work to the carb bodies, especially:

- polishing the piston bore for silky smoothness.

- repair or clean up of any stripped threads in the carb bodies.

- replacement of any damaged or worn parts. In fact, the ability the recognize what is damaged and worn (besides the parts above which are designed to wear out) is the most difficult part of the entire task, since it requires a level of experience: are my needle tips worn? What, exactly, does a worn needle tip look like? How "smooth" is smooth enough? Etc. This is where the advice and experience of the members of this forum are invaluable.


c) Proper "settings" of the various components during re-assembly:

- the float heights

- the "basic or bench synch" of the throttle valves


d) On-bike "settings":

- first and foremost, the measurement and setting to specifications of the valve train (shim) clearancs. Failure to do this "wastes" 90% of your efforts involved with the carbs.

- final synch (using some type of mamometer and the YICS tool if your engine is YICS-equipped)

- idle mixture screw setting, preferrably using a Colortune plug.



I get the feeling from reading many posts that people believe that because these bikes are inexpensive to PURCHASE, that they are inexpensive to MAINTAIN or REPAIR. That is the wrong, wrong, wrong; a VERY BAD idea. Thinking like that will inevitably (almost 100% guaranteed) lead to frustration and added expense.

Among the many nice traits of these bikes is that they actually are simple enough for the average person to work on and to do repairs on SUCESSFULLY by themselves, as they were a pretty well-engineered design (except for the fusebox!) and very durable, easy to work on.

But "easy" doesn't mean "cheap" and if you are willing to skip steps in order to save a dollar or two, or a minute or two, then in many cases you're going to be doing that old Fram oil filter commercial thing: "you can pay me now, or you can pay me later". And that "future payment" is going to involve a lack of performance and more time and effort on your part until you eventually just give up, or buckle down and do things right.

The rule of thumb in the boating or aviation world is this: whatever you paid for the vehicle, expect to spend 10-20% per YEAR of that purchase price in maintenance costs. Just because you could "afford" to buy the vehicle doesn't mean that you can "afford" the yearly preventative and service maintanence costs; and if not, well, then eventually you learn quickly why people say that a boat is just "a hole in the water that you throw money into". That's not really true, but that's what people who don't understand that on-going PROPER maintenance and repair costs need to be factored in when determining the real "price" of a bike, especially an older one which is going to require not just the normal on-going maintenance costs, but most probably also additional costs to make up for the previous owner(s) lack of proper maintenance.

The issue that arises with older vehicles is that the purchase price is quite low. That's a blessing, in some ways; but in other ways, that's bad because it lulls people into the belief that the maintenance "costs" (time AND money) will be cheap too. A MUCH BETTER WAY to understand it, I believe, is like this: IF your 1982 XJ650 Seca could be purchased BRAND NEW, today, the price would be $X (let's say, $10,000 ?). THEREFORE THE ANNUAL MAINTENANCE COSTS WILL BE $1,000 - 2,000 PER YEAR.

And never mind that maybe you get "free oil changes and service/maintenance" as part of a new-vehicle "warranty"---you PAID for those "free" maintenance costs in the purchase price of the bike, rather than in smaller chunks on down the road. In fact, "free" service warranties are really just a way of allowing a new vehicle purchaser of FINANCING those service and maintenance costs into the purchase price, rather than paying cash every 6 months for those maintenance and service fees.

And many (most?) OEM vehicle sellers make more money off their customers from those financing charges (assuming a purchaser finances through the OEM financing program, which most people do) than they make off building the vehicles! THAT'S why they offer the "free" service to you, so they can build up that purchase price, and thus financing fees, by "hiding" the 10-20% additional yearly costs into the purchase price. This gives people the completely wrong ideas and understanding about what the true, REAL costs of vehicle ownership are.

On used vehicles with no "free" warranty, those service and maintenance costs become very real, very quickly.

I understand and appreciate that some people are going to wildy disagree with me on the above statements, and that's cool. And since I offer parts for sale (for these bikes), many will say that I'm just trying to push people into spending needless amounts of money. Well, that's one possibility.

The other one is that the OEM enginners and manufacturers and experienced (honest) mechanics will also tell you pretty much exactly what I'm portraying here: doing things right actually saves you time and money in the long run, and that all complex mechanical objects (from your lawnmower on up) requires periodic, proper maintenance if you expect it to perform to the level it was designed to perform to, and have the life expectancy that it was designed for. These things aren't magic. They aren't due to luck. Having a bike perform properly is not akin to winning the lottery, i.e. some people get lucky and others don't and that's just life. If you dig deep, if you could stand over the shoulder of those who are successful and those who aren't, the ways in which success is determined are pretty clear-cut and straight-forward, as outlined above.

As are, unfortunately, the ways in which a lack of success are achieved.

 

Chacal.....
Holy Cow! I've never heard The Truth spoken so profoundly or eloquently! Can I copy this post and take it to work for my cheapskate customers to read while they whine and moan and wring their chalky-white little hands? Man talk about hitting the nail square on the head!
You have struck upon the basic truth of All Maintenance....cheapskates believe, invariably, that because they purchased something cheaply or inexpensively, that the subsequent maintenance of that object should follow suit!
Will, listen to these guys. They know of what they speak. Right now, you have to make one of two very basic, but important decisions;

1) Sell the Seca and buy a Brand New motorcycle, complete with factory warranty, roadside assistance, and everything else a dealer can heap on you in exchange for the Almighty Dollar. Many folks go this route, and there's nothing wrong with it if you can afford it.

2) (a) Keep the Seca, buy a good (read; factory) manual for it. Visit here often. Ask questions of folks like Rick and Len and others and take their advice to heart. Don't be afraid to learn or try something new. You will be a better owner and rider as things begin to click
(b) Keep the Seca. Find a good, experienced mechanic to work on your bike. Pay him. Pay him well, and in a timely manner. Tip large, too!

Remember; you can't get something for nothing. If you got a steal on the bike, you've already got your savings.

 

Ay Captain, you may. But be gentle on the customers.....remember, they've been "trained" to think in a different manner, that's why they don't understand things!

One last thought about these carbs, since they are THE most troublesome aspects of these bikes, and something to consider:

- the four carbs concept is really neat looking, and certainly performance oriented to the extreme.

- for many of us who had lots of experience with automotive carbs, just beware that while these Hitachi and Mikuni carbs are a bit different in operation (and thus parts), a carb is a carb, and they're pretty basic little devices. The main difference is that the passages on these carbs can get bizarrely tiny, especially if you're used to working on automotive carbs (which have canyon-sized fuel passages compared to these carbs).

- like I've said, the cleanliness part is really just tedious work, with a couple of "tricks" thrown into the mix, given the small sizes you're having to deal with. The "rebuild" part is basic mechanical knowldege and skills, knowing which way to turn a screwdriver to loosen vs. tighten, when and how much force to use or not, being organized, stuff like that.

- but the "tuning" part will require some special tools, but no type of any rocket-science knowledge or skills----once you master the rebuild and tuning process with these bikes, you are pretty much a Carb Tuning God, as these carbs are about as "complicated" as it gets with carburators. I mean, VERY few vehicles have multi-carbs, not until you get to the really high-performance machines level in the automotive world.

- well, as "complicated as it gets" until you start adding pods, etc.----which if you do, I sure hope you've got every last one of the basics listed above down to a science, and you can do it all, properly, and blindfolded, too..

- finally, if you do not have a service manual(s) for your particular bike(s), and you're going to wrench on it and want to do things right, then the only thing I can surmise from such a course of action is:

a) you're already an expert, or.....

b) you aren't really serious about doing things right, and that's okay, too---just don't expect good, quick, or cheap results!

 

Don't worry Will, we're not picking on you. These comments are directed generally to the scores of folks (like me) unwilling to wait weeks and pay hundreds to a shop for something I can do myself. You are to be congratulated on your first bike and your first job as a shadetree mechanic! 8)

I just went through this myself. I tried to get my bike running this time *last* year and ended up parking it all summer. It took about the fourth time "cleaning" the carbs before I noticed all the other problems like vacuum leaks in in the carb holders and a leaky needle valve that made it *impossible* to properly adjust the idle mixture. I often try to pat myself on the back for saving as much money as I can, but sometimes it's just cheaper to buy new parts when you factor in your time and frustration.

The other thing is tools. You wouldn't try to use a pipe wrench to remove spark plugs, you're not going to be very successful in tuning your bike without a Colortune and a vacuum sync tool. Or let me rephrase that, *I've* been woefully unsuccessful tuning without a Colortune and a sync tool. Maybe some of you guys can do it by ear/feel but I'm a loooong ways from that. It may seem bass-ackwards to "save" money on shop fees just to go out and buy a bunch of expensive tools... the savings come next year when you already have the tools and they pay for themselves.

Will if you can find someone nearby in NH with the necessary tools and experience, they can probably get you going for a 6-pack or two. Otherwise, all I can suggest is what I did: buy the repair manual, read it cover to cover, buy or make some tools, order up some parts online for cheap, and get dirty. If you're running lean, the wrong thing to do is start playing with your idle mixture (pilot) screws. Step one should be removing and cleaning the carbs, then check that the petcock allows plenty of fuel flow, check the needle operation and adjust the float level, check your carb holders for vacuum-leak-causing cracks, reinstall and sync the carbs... and then you can think about richening the mixture if it still backfires. I've tried it the shortcut way, and I ended up lost in the woods. For a year. Don't make my mistakes.

 

Tylernt hits one out of the park and tells it like it is!

Also, when you do get the tuning tools, the biggest PROBLEM you'll run into is that you'll be tempted to play with them all of the time, constantly tweaking and adjusting and basically, just playing with them, especially the colortune plug, cause it's just so damn neat to see each individual "burn" going on inside of your cylinders..........

Oh, and in case it was mis-understood, in NO WAY was I trying to pick on you Will, or criticize.....just trying to tell it like it is, so that YOU will have the information available to you to make what is the best decision for yourself.

 

There you go Will, darn good advice all the way around.
Do not fear the job, embrace the opportunity to expand your experience in life (and get a durn good feeling about doing it yourself!).
You go for it (with the right tools and books). Heck, if Rick were as near to me as he is to you, I'd never come home. There are just too many XJ's to twiddle.

 

I charge more than a couple of six-packs to Clean and tune.

But, I'll be happy to talk about if for the price of a couple of six-packs.

My take is like those pretty gals say about Loreal Products.

I might cost you a little more than a 2, 6-pack guy ...

But, ... "I'm worth it!"

 

My name is Kevin and I'd like to chime in on this thread?

I just purchased a 1983 Maxim 750 from a close friend of mine (whom I watched struggle to keep it running for two years!) and now I know the pain that is retuning one of these YICS bikes. He pointed me to this forum and I read and read till my eyes where bleeding before I jumped into fixing this bike. And I'll tell you what! Buy or make the tools, get replacement parts and love your ride. I've got this thing running and am already fine tuning with it. I let die hard (harly) bikers ride this Yamaha and they all can't believe how comfortable and how nice it rides.

Rick, Chacal, Len and evryone else on here, THANK YOU, you made my life just a bit easier!!!!!!!!

 

Kevin, you're quite welcome!

Regarding Rick's comments on the price of carb work, let's look at it this way:

Cost of basic PARTS needed to fully rebuild carbs, assuming no missing or damaged pieces: $ 100-150 (idle mixture o-rings and washers, float valve needles and seats, bowl gaskets, replacement bowl drain screws, throttle shaft seals, fuel tube o-rings, and misc. parts). Starting adding more $ if you need fuel jets, air jets, emulsion tubes, enrichment circuit parts, intake manifolds, airbox boots, or any hardware (screws, washers, missing brackets, clamps, etc.). Keep going if you replace the fuel line, vacuum line, add that in-line fuel filter, and keep a C-note in reserve (no pun, really!) for the petcock overhaul.

Cost of basic TOOLS needed if you don't have them: $ 100- 200+ (colortune plug, synch sticks, YICS tool, proper JIS-spec screwdrivers, valve shim bucket tool, etc.).

Cost of TIME:

This includes removal, COMPLETE rebuild (meaning breaking the rack so you can replace the throttle shaft seals), and install and tuning.

a) the first 3 times you do it: 25-50 hours, depnding on how many shortcuts you take, which actually determines how many times you're going to be doing it before you get it right.

b) the next couple of times you do it: 15-20 hours.

c) Once you're an expert (like Rickomatic, etc.): 10-16 hours, depending on what items are missing, damaged, need special coaxing, etc. (Rick chime in if your figures are different!).

d) The above times and prices do NOT include the valve shim clearance checks (3-6 hours) and replacement(s) (another 2-4 hours unless you already have the shims on hand, in which case subtract 2 hours), and which should always be done before or as part of a "carb rebuild" because you can't synch the engine without the valves being in proper adjustment, and if you can't synch the engine they you can't tune the carbs, unless you're into wasting time and money in a major way.


Now, what's the going labor rate at most shops? Let's say $50 per hour.
So, labor costs at a typical shop using the LOW END in hours are going to be:

$ 50/hour x 10 hours = $500

Labor costs for an expert should be more; expertise is worth a bit, since it will get done really, Really Right the first time around:
$ 65/hour x 10 hours = $650

Don't forget to add in the parts costs, AND the (one-time) tools & equipment costs if this is your first rodeo.


Earlier in this thread, I wrote up a little sermon on the cost of maintenance on vehicles, and how that cost is vastly and sadly overlooked by 1st time owners, especially of these older bikes (that many shops refuse to work on, and even if they do, you may end up wishing they HAD refused to!) because it's tempting to get seduced by the allure of the low purchase price.

It's always worth a read for new owners. I promise you it's true.

 

The Dealerships in New England are closer to $80.00 / Hr.
That's why I say buying the Factory Manual PAYS for itself as soon as you crack the cover and do anything for yourself.

You can't really say how long doing a Carb Overhaul is going to take. Every set of Carbs poses different challenges.
Especially, if there's been damage done by someone who has been in there before you and tore-up the Jets or has buggered the Pilot Mixture Screw tops until almost nothing is left.

Some Carbs need only be treated with spraying and wiping-out.
Other are so bad, that you have to let them soak in cleaner overnight or attack the blockages with cleaning tools.

I usually spend a minimum of 8 Hours doing a Cleaning that does not involve have to take the bodies apart.
If the rack needs to be split for Throttle Shaft Seals -- that's another four hours if there's NO complications.

25 years time cane set-up some serious complications when you decide to do a complete Overhaul.
Fasteners and screws that have never been disturbed in all that time are often reluctant to come undone.

But,, having the right tools and knowing how to handle the obstacles makes it just a little bit easier.
Once you get into a complete Overhaul and bring the Carbs down to bare minimum, you understand the volume of work involved and are less inclined to ignore the need to keep them in a cleaned state.

 

Guess I'm glad I just have a twin... half the work! Actually I bet it did take 8 hours my first time, last time I did it in 2 though there were no time-consuming complications.

I can't agree enough.

 

Rick and Len; AMEN. And it is very true, it is much cheaper to do it right the first time even if you end up buying a 'bit' or two you didn't use...you'll need them eventually, put 'em in your "Yamaha" drawer. These bikes were marvels of the engineering available at the time, and PROPERLY maintained will last a long time. Unfortunately for most of us, myself included, finding one of these gems that actually HAS BEEN properly maintained for the last 25+ years is nigh onto possible. We get to pick from bikes that have either been A: NOT maintained, just ridden or worse yet, allowed to SIT, improperly prepared, for years, or B: Have been "worked on" by infidels with no clue as to what they have in their hands. I personally prefer "unmolested but rotted" rather than "tinkered to death"--nothing irritates me more than screws that appear to have been chewed by wolves. Chacal is right about the bottom line; proper upkeep on a Classic XJ Bike is not cheap; I have already more than doubled the purchase price of my first Seca just getting it roadworthy, but it is now worth FAR MORE than "the sum of its parts." It also requires a bit of an investment in tools, time, and the acquisition of new knowledge. (So great an investment in my case that it pursuaded me to buy another XJ...) You have to look at the overall cost of ownership; yes these modern classics can be had cheap, but KEEPING 'EM CLASSIC is a different story. Wanna talk about total cost of ownership of British bikes?

 

Anybody reading through this entire thread has been treated to some of the truest words and best advice about vehicle ownership and mechanickin that I've ever seen. I spent years working in a general auto repair shop where we worked on everything from crappy K-cars to Panteras, Corvettes and other wierd stuff. I tried to teach my kids that finding a good mechanic was just as important as finding a good doctor - besides the only procedural difference between the two is that the mechanic washes his hands before he uses the bathroom!

I've been around and ridden bikes since I was able to drive and have had my Seca 550 since it was brand new in '81. But I was a bad owner and the bike has set forlorn for 20 years. It wasn't stored properly and I knew the fuel system was going to be a nightmare.

I read everything I could find on this forum (already had my 27 year old factory service manual) and did one more thing before tearing into the carbs - I bought an ultrasonic cleaner. Been wanting one for years, and this was the perfect opportunity. Good thing too, becasue without it, dissambling some components, to say nothing of cleaning the carbs, would have been impossible. That is no exaggeration. I'm sure other folks have carbs much easier to clean then mine; I'll post some nauseating pictures later.

I ordered the required parts from Chacal and got everything from the inside of the tank to the float bowl drain screw o-rings. I'll probably be ordering the synch sticks and color tune prior to making it run again, but I am so excited to see the absolutely, surgically clean carbs going back together. Oh, and even though I've worked on all kinds of other stuff, this is my first venture into multiple little Mikuni land, so until it all runs and runs right, I'm still a beginner and have a lot to learn! So, far I know of no better place to learn - than right here...

Finally... Will, don't be afraid to learn. Don't be afraid to break something -it's just stuff. If you don't try, you don't learn. For any of us, learning just means overcoming ignorance! If you decide you don't want to work on it yourself, then reach out to the guys that CAN and DO, and celebrate your decision, but like a good surgeon, be prepared to pay a fair price for the knowledge and skill the man has spent his life developing.

 

^^^^^Amen brother!^^^^^

 

no7h1ng, you lucky s.o.b. I wish Rick O was 45 mins from me.

 

^You an me both mate!^

 

Reading all of this makes me think that the wise thing to do is to purchase a second set of carbs that you are working on to get perfect and to have them as an annual swap-out with the ones on the bike and go back and forth ...

 

Buying a set of used Carbs at a reasonable price is truly a GREAT investment!
Even it they are filthy they can restored and either used as a cleaned and ready to go "Swap-out" ... or, just for Parts alone.

I have had to buy a whole set, on occasion, just to grab a Carb Body without a broken Hinge Pillar.

You usually get a set with rotted-out Chromed Tops and Fuel Bowls that look like a Chain-Gang spent the week tarring them.

Keep in mind, if they come with four Diaphragm Piston Assemblies that are not dry-rotted and pin-holed ... you have a set of replacements to keep your GOOD set running right for years to come.

If you luck-out and get a set that just needs somebody that knows what they are doing to give them the thorough cleaning they need; you turn somebody's cast-offs into a valuable learning tool and a major asset for yourself after you get them cleaned and rebuilt.

 

This is a great thread and should be mandatory readingfor all newbies. At least make it sticky, or even a FAQ about "Care and Feeding of an Older Vehicle".

Well stated all around gentlemen.