Hello. New here and have SEVERAL questions.

Hello everyone. I'm new here and want to introduce myself (and bike of course).

I'm Jeff. Been an auto technician for over 20 years. long enough to know a bike isn't a car.

I have a 1980 Maxim I 650. I've had it since last August, and have recently started riding it again.

I have several questions, but I am going to start with the fuel system.

A quick history: I live in Denver CO, The bike had a major service the year before I got it, but sat for most of the time afterwards. It has supposedly been re-jetted for the altitude but I have been reading the posts here and am starting to wonder if it was done.

Two things I have done are the backyard carb balance trick (tying the carbs together with vacuum hose), and I had to adjust the idle jets (I'm guessing on that. (With the tank off, the carb screws in the forward front corner of the carbs. They were way off for a smoother idle. Went about 2+ turns counterclockwise on each to get a reasonable and smooth idle.) I checked the plugs first and had a rich mixture. It idles much better, always been pretty easy to start w/max choke cold, fine warn with no choke. I have a surge/poor acceleration in 5th gear at highway speeds (about 65-70 and up) and speed loss going up slight hills. I can down shift into 4th and it smooths out. Any thoughts on main jets being to big, an adjustment for the mains?

I know auto carbs, but never really worked on side draft units. Yet

Thanks in advance,
Jeff

P.S. I'll have more questions after I read more on the site and get dirty hands on my bike.

 

Welcome to the site Jeff. I have no idea....does that help? Ha! I am the resident expert on crying when someone says "Remove your carbs...". Im sure you will get plenty of dead-on responses very soon.

 

Welcome Jeff!
Post your jet sizes, someone can tell you if you have had the jetting done or not.

 

Welcome to the forum. Let me start out by saying. If you need help you have come to the right place. I and another ej'r "pardyboy" from Denver are going to get together in the next couple of weeks and get his bike tuned up as well. You are welcome to join us. I have the tools we need for the carb tuning and I would be glad to share some of my knowledge on these bikes with anyone willing to listen. I am no expert by any means but love to work on these bikes. Shoot me a PM with your phone number and I will call you and him to get something set up within the next two weeks. Kind of a mini carb tuning party. Have a good one.

 

Thanks for the responses.

I won't be cryin about taking the carbs off. It'll be a few other choice words that I won't be able to post here.

I would love to post the jet sizes, but I have no clue yet.

Another clue - I tried giving her a little choke after she was warmed up and as I was going down the highway. I got a little more power and she seems to smooth out a little more. I'm thinking that the jets may have been replaced but not correctly. Do the jets allow more air, gas or both depending on which jet?

Thanks for the start, ttyl,
Jeff

 

Welcome Jeff!

In my opinion, the first thing you need to do is get a "carb-tune" tool to sync the carbs.
OR make one.(there are numerous posts)
Getting the carbs balanced is critical, then you can worry about the mixture of each one.
As you change the mix, you will have to re-sync the carbs (sync, mixture, sync)
The other good tool that many use is a colortune plug which actually allows you to see the flame inside the cylinder to determine if it's too rich or lean.
IMO, you can get the mixture "close" if you have a good ear, but syncing the carbs is vertually impossible without some sort of tool.
Basically you need to get each butterfly EXACTLY the same position so each cylinder is drawing in the same amount of air/fuel. If it's off, you are flooding one cylinder while the others are starving.

I'm sure your local fellow XJers have some tools and expertise to share.

Good luck,

 

Jeff:

From you Posts I'd say you have to do some work to insure that the Diaphragm Pistons can react to Manifold Vacuum without hesitation or binding.

On Carbs over 10-years old the Bore (Cylinder) that the Diaphragm Piston travels in gets oxidized on its O-D ... thereby shrinking the circumference just enough to have the Pistons bind, hesitate, shutter-up and down rather than rise and fall freely.

Refinish the Bores that the Diaphragm Pistons rise and fall in.

At the base of the Diaphragm Piston is a Needle Valve. The Needle Valve extends into an Emulsion Tube which is surrounded by as many as 18 to 20 Air Metering Pin-holes.

The Pin-holes in the Emulsion Tube regulate the Main AIR that passes through them to allow the rush of Intake air to draw-up an emulsified stream of Fuel from the Main Jet.

If any of the Air Holes in the Brass Tube are clogged ... performance suffers.
The Tube is a press fit. Presses out the top after removing the Main Jet and washer.

Look at the O-D of those Tubes and see if you can see light through the holes drilled straight through the other side.

If you are a big guy, you can up the Main Jet a size and get a little more pulling power along the highway.

 

Thanks everyone. I now have a good idea of where to start. Now I just need to get all technical info locked into memory and I'll be happy.
I'm going to get with samsr and he's going to impart as much of his knowledge as I can remember.
I'll update as I go.
I think I got a very good bike to work with. Mainly stock as far as I can tell and always maintained. Just needs a couple updates and she'll be good.

 

Hey everyone. Have an update. I finally had the nerve to pull the tops of my carbs off. The jets on the top side are 195 and 50. I am assuming those are the pilot jets.
Is it normal to have fuel on the top side of the diaphragms? I had 3 of 4 carbs that had gas on top.

Thanks again,
Jeff

 

Those top side jets are correct for your carbs, but they are really the main (#50) and pilot (#195) AIR jets. Your FUEL jets (#110 main) and (#40 pilot) are down below, in the bottom of the carb body, and are those large "mushroom-head" jets as Rick has pictured int he photo above.

And no, you really shouldn't have fuel up there!!!!!

 

Thanks chacal. Are those stock for sea level? I'm in Denver at about 5k altitude. I found a post on here about jets and altitude, as well as aftermarket add ons but can't find it again.
At the risk of showing my novice ability with these carbs, are the pilots for low rpm and the mains for high rpm? If so, at what rpm do they transition?
And how do they get fuel up in the top side of the carb?

Thanks,
Jeff

 

Hey JT, here is some info about re-jetting, including some formulas for altitude adjustments:


WHAT ABOUT RE-JETTING FOR PODS, ETC?:

It's a question we get asked often and unfortunately, one that we cannot answer honestly about your specific bike besides with "it depends".

Which is a nice way of saying "you're about to enter the seventh circle of hell......."!

Carb jet tuning required by aftermarket modifications is somewhat of a black art, part science, part skill, part luck. It depends on the current state of tube of your engine, your altitude, the mix of aftermarket parts on your bike, etc........alot of variables.

The best advice we can offer is: Just Say No. Don't do it! Leave eberything stock!

But, since most people---with good reason, I might add---don't always listen to our well-intentioned advice, then the next best recommendation we can offer is: "if you want more power get a bigger bike!".

And that doesn't cut it with many riders, either, so for the remaining stalwarts out there who insist on "experimenting" with aftermarket intake and exhaust systems, here's the best information that we've come across to give you some GUIDANCE, which you should take as just that, and not as ANSWERS, because it isn't!

We wish you luck with your endeavors!

******************************************************

Hi xyz!.....we've never used pods on any of our bikes, they just seem like way too much trouble to me! BUT, here is the "standard" re-jetting recommendations from people who fool around with them....although, please be aware that every situation is different, and you should expect to go through some amount of trial and error (and frustration!) before you get it as close to right as is possible.

By the way, the most important part of the information below is in the section titled "PRECAUTIONS"!:

So here is the info regarding jetting that you might find helpful:


MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:


Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

+4 main fuel jet sizes for 4-into-1 exhaust

+4 main jet sizes for no muffler (open headers)


Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

+2 main fuel jet size for drilling holes in the airbox

+4 main fuel jet sizes for individual pod filters (no airbox)


Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.


PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.



PRECAUTIONS:

- Make sure your carbs are in perfect working order before making jet changes....meaning fully cleaned internally and rebuilt.

- Check plug color often and adjust as needed, 2 main fuel jet sizes at a time and 1 pilot fuel jet size at a time. Bright white plug insulators are a sign of an overly lean fuel mixture condition and WILL cause damage to your engine over time, up to and including engine seizure!

- Synch the carbs after each jet change.

- Make sure the floats are set correctly

- Seriously consider purchasing a Colortune Plug Tuning kit.

- You may find it necessary to make changes to the size or shimming of the main jet needle. There are no guidelines on what or how to do these changes, this is true trial-and-error tuning!




EXAMPLE:

Stock Carb Settings:
#120 Main Fuel Jet
#40 Pilot Fuel Jet
Y-13 Needle

MAIN FUEL JET SIZE CALCULATIONS:

Changes made:

Exhaust:
4 into 1 with Supertrapp = +4 Sizes Main Fuel Jet

Intake:
K&N Pod Filters = +4 sizes Main Fuel Jet
----------------------------
Equals: +8 main fuel jet sizes baseline
Subtract: -2 main fuel jet size per formula above
----------------------------
Equals: +6 main fuel jet sizes due to modifications, thus:

Stock main fuel jet size is: #120
+ 6 additional sizes
= a #126 main fuel jet size
---------------------------
Subtract: -2 main fuel jet sizes for Altitude of 2500' Average

= #126 calculated from above
-2 jet sizes for altitude adjustment

= a #124 main fuel jet size.


PILOT FUEL JET SIZE CALCULATIONS:

The formula is: +1 pilot jet size increase for every +3 main jet sizes increased.

Stock pilot fuel jet size is: #40
+ 2 additional jet sizes (since we went up +6 main fuel jet sizes before the altitude compensation was factored in)

= a #42 pilot fuel jet size.

Note that no altitude compensation is needed on the pilot fuel jet since our elevation is less than 6000' asl.


------------------------------

RESULT:

A #124 Main and #42 Pilot is A GOOD STARTING POINT.

******************************************************


The holy grail of carb tuning information can be found here:

www.factorypro.com


I don't know why or how fuel is getting into the upper areas of the carb body (above the diaphram, but all I can say is that it is a Very Bad Thing, and needs to be resolved. Perhaps some other members can chime in with some thoughts on that subject.........

 

fuel never gets to the top of the carbs, except for the idle and enrichment circuits, which dump fuel through tiny pinholes right above the butterfly.

You're mostly right on the pilot/main jets. Pilots give you idle through about 25% throttle, at which point their function gradually tapers off. From there, the combination of needles/emulsion tubes/main jets takes over. From about 25% to 75% or so, the fuel is metered by the jet needle inside of the emulsion tube. The taper on the needle allows more fuel to be drawn up as the needle comes out of the emulsion tube. From about 75% to WOT, it's all main jet.

 

Mike, I pulled the diaphragm pistons out today. They felt smooth in the bore. I carefully buffed them with some steel wool to get them smoother. I am guessing the pistons have a coating of some sort, so I didn't go crazy with the steel wool. The bores look very clean. Nothing on the sides. Nice and shiny. I have played with the mixture a little and think I may have made things worse. (of course, That's the way I roll. )
She still runs ok, just not as well as I'm thinking she should. Still have an odd power drop at higher speed. I feels like a float issue. It's almost like it runs out of gas for a second then comes back. What confuses me is I down shift and it feels fine/better.
Thanks again for all the info. Samsr is coming by tomorrow and we're going to play with the bikes. I'll post an update.

Thanks again everyone,
Jeff

 

Wow. You guys ar good. Thanks for the quick answers. What I've been told is my carbs have been jetted for the altitude. Everything else is supposed to be stock. Good thing I'm broke. I can't play with them even if I wanted to.
I am going to leave every thing as is and just keep her properly tuned. The only thing that gets me is the surge at high speed. It just doesn't seem right.
Speed is fine for me with this one. I know she can only do as much as she can do.

Thanks again,
Jeff

 

Jeff,

You have the right idea - work with what you have.

You really don't need to do anything to the jetting for the altitude here on a stock bike. CV carbs are not that sensitive to elevation change.

Back in the 80's, I ran stock jets in my 650 Maxims without any issues. I bought one of them new in San Diego and it ran great here without any jet changes.

The Seca I have now still runs with stock jetting and doesn't have any problems, even up on the Peak-to-Peak Highway.

BTW, you should feel bad - trading an Escort wagon for a great bike. Sounds like you made out on the better end of that deal.

 

A surge is an indication that the Diaphragm Pistons aren't lifting in unison.

You might want to Polish the Diaphragm Piston Bores after de-oxidizing them.
Another reason for surge is Pinholes in the Diaphragm Rubbers.

Sometimes the holes are quite obvious.
Others require a thorough exam of the Diaphragm Rubber.

If you had gas above the Diaphragms ... look closely at the Rubbers and paint on some Liquid Electrical Tape over abrasions and cracks.

If the Diaphragms are not pliable ... coat them with Teac Rubber Pinch Roller Conditioner to bring-back the suppleness of the Diaphragm's Rubber parts.

Also be sure that the Diaphragm is "Seated" all the way around in the groove. A pinched-off edge or a misplaced rubber seal will negate that Diaphragm's ability to respond to variations in Manifold Vacuum.

 

You'll have to see my bike to know how good i made out Jim.
I'll leave the jets and carb set up as is, Rick.
Just a feeling that I shouldn't play with this one. Shes too right.
How do I check the diaphragms for problems? (I know, ask her. If it's blue, Run!!)
They all look good, almost new. I'm hesitant to mess with them too much. I can see myself pulling too hard and making a hole. (Unlike pushing too hard into the hole.)
I made sure the rubbers were aligned. Very nice of the engineers to put on a locating tab. (fur-less is so nice.)
Can the pistons not be in unison at higher 5k+ rpms? If so, what's the area to check? All the main needles are rated as 10s. Haven't pulled the bottom of the carbs yet, so i can't tell what they are.

Thanks,
Jeff

 

The top end of the Carb is the easy part. After the Cover comes off; everything is exposed.
If you have the tops off, you might as well do a cleaning of the Piston Bore.

After all these years its not uncommon for the Bore to get oxidized on its Inside Diameter. The dull, gray coating isn't conducive to having a moving part within it.
Some people say the oxidation actually shrinks the tolerance between the Piston and the Carb Body.

It definitely causes the Piston to act funny.
Either chattering up and down, hesitating or worst case ... getting stuck.

I sharpened the inside and outside diameter of an old, beat, 19 mm Socket and use it as a tool for punching-out little wafers of ScotchBrite Pad.

I put seven of the cookie-cuttered ScotchBrite Discs on a Dremel Bit with Pop Revit washers and External Star Washers to keep them tight to the bit for high-speed scrubbing-out the Diaphragm Piston Bores.

On all the Carbs that Members have sent to me for cleaning, I also Polished the Bores to make for a frictionless inside surface that allows the Diaphragm Piston to rise and fall effortlessly.

You want that.
You want the Piston to rise and fall with the variations in Manifold Vacuum for top performance!

 

Update: Samsr came over yesterday and went through the carbs. The only concerns were 1 idle circuit holes may have had junk in it and one main had some crud. The floats were all a little low. Everything was pretty clean and didn't take much to get them all right. (Randy's good.)
Haven't ridden enough to check fuel mileage, but I know it's going to go up.
The top end if fantastic and the idle is nice and smooth. One thing did come up that wasn't there before. The transition from idle to about 2k is lagging. It feels like it getting an extra shot of gas and I have to clear out the excess before she smooths out. I have my plugs at about .30' gap, the air filter is stock and clean, the jets are all stock. I forget the numbers, but i think the the gas jets are 40 and 110? the air jets are 50 and 195.
Other than the lag, she screams and I have to change my riding style. Not as much WOT operation.

Thanks again Randy,
Jeff