'82 Seca 750 popping sound

Hi it ran perfect until about 3 miles up the road when I went to turn around it stalled and I had a hard time getting it running. It wouldn't start unless I let it sit for about 60 seconds and then it would start with the choke on 1/2 way but I couldn't keep it running. So finally after many try's I got it moving and it ran good going back. When I got home again it idled fine and started up good. I drove it again and it worked fine. Later in the day it acted up again and there is a popping sound coming from the left exhaust so I checked the plug and the left outside one was blacker than the rest but dry. The carburetors are clean and set right except they haven't been synchronized since they were cleaned. BUT that part of the carbs was not touched during cleaning. DO THEY STILL NEED SYNCHRONIZATION????
Also would a bad plug wire cause this problem?

 

Yes, they absolutely need to be synced. The black plug can come from too lean, but usually from too rich. If unburned fuel gets in the exhaust it can ignite causing the popping, which is very common for lean settings. If you have a colortune plug use it to set the pilot screws. If not, most folks start at about 2 1/2 turns open and adjust from there. Also, are you sure the petcock is delivering enough fuel to the carbs? Or even a clogged vent on the gas cap? Either of those might cause the stalling after a short ride. If it stalls again set the petcock to Prime and see if it starts. Next, open the gas cap and see if that helps.

 

Ok. First of all THANK YOU SO MUCH. That's an excellent start. I'm going to synchronize the carbs. But my problem is intermittent. Can Unsynchronized carbs cause an intermittent problem. I would think that would be a consistent problem.
Also the carbs don't have external adjustments except for the synchro adjustment, I don't think
The jets are a fixed size. The only adjustment is the floats.
Could it be a bad wire? Because they are old.

 

ohm out your ignition system takes about 15 minutes

The Ultimate Relay, Switch, Sensor, and Diodes Guide


XJ750 air-cooled models:

Pick-up coils:
650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range


Ignition Coils:

Primary side (input from main wiring harness):
2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

Secondary side (spark plug wires, without their end caps):
11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range


Spark plug caps:
1981-83 models: 5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range
1984 RL models: 10K +/- 20% = 8,000 to 12,000 ohms per cap acceptable range

Spark plugs:
0 ohms per plug

 

the air mixture screws are under caps and could need adjustment

 

Oh yeah. I forgot about those Bummer.

 

Replace "and could" with "definately do".

Carolyn, if the mixture screws weren't removed, then the carbs aren't clean enough. If they were removed they shold be set to a baseline of 2.5 turns out from being gently seated. Typically they get opened up a bit more from there; to around 2.75 to 3 turns out. Bump the screws the width of a dime as you set the idle mixture, as little bits make fairly big differences.

 

Ok. I thought that I knew what you meant, but when you say "caps', do you mean little limiter caps (much like a tiny tiny frost plug), or do you mean the chrome caps on top of the carbs?
Also are you talking about Mikuni carbs or Hitachi carbs?
Also thanks for being so patient with me. I have been working on many different projects I'm getting my carbs confused.

 

on the top front of carbs there is a little seal disc the mixture screws are under them . sealed at factory for EPA reasons

 

Ok that what I thought. And that's on the Mikunis?

 

go to this link
http://www.xj4ever.com/inside your carbs.pdf

do you see the screw at the 6:00 position thats the mix screw on hatachi to right of enrichment plunger

 

should be hatachi and mikunis

 

Oh thank you. Could you tell me the number on this diagram?

 

It's on both, and your bike has Hitachi carbs (well it's supposed to anyway).

They are #26 in the diagram you posted, but are found just to the right of the enrichment plunger in the pic XJ550H posted (the caps are missing but you can see the slot in the mixture screw).
The caps do not need to be replaced once removed, but Chacal sells rubber dust caps if you want to cover the screw heads.

Out of curiosity: do you have an inline fuel filter fitted to the fuel line?

 

# 26 is the enrichment rubber cap not mixture cover

. . Cover, Plunger Cap 4H7-14173-00-00

mixture screw set up
it is not shown in the drawing.
there is a brass or aluminim cover the mixture screw a spring, an oring and flat washer.

it is not shown because it is only supposed to be serviced by factory

 

Ok

Yes I have an inline fuel filter. My 1982 Seca 750 has Mikunis but my 1985 maxim 700 has hitachi carbs. Yamaha Parts list, by application, says the 1982 Seca 750 has Mikunis. I THINK That diagram I posted is definately the carbs on my bike though.

 

http://xjbikes.wikidot.com/carb-specs

this is what you should have in the 82 seca 750
XJ750 Models:

Years & Models: 1981-3 XJ750 Maxim, Midnight Maxim, and Seca USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 15R00 (Maxim, Midnight Maxim)
Carb Model ID: 5G200 (Seca)
Main FUEL Jet Size: #120
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #80
Pilot AIR Jet Size: #225
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-13
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

is the 1985 maxim 700 water cooled? or air cooled

XJ700 Models:

Years & Models: 1985-6 XJ700 air-cooled models
Carb Manufacturer: Hitachi
Carb Series: HSC33
1985 Carb Model ID: 1FG00 (N models) or 1JJ00 (NC models)
1986 Carb Model ID: 1NH00 (S models) or 1NK00 (SC models)
Main FUEL Jet Size: #107
Pilot FUEL Jet Size: #36.5
Main AIR Jet Size: #70
Pilot AIR Jet Size: #210
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #36 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-20
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 1.0mm +/- 1mm (.039" +/- .039")
Idle RPM's: 1,050 rpms

Years & Models: 1985 XJ700-X XN/XNC water-cooled USA models
Carb Manufacturer: Mikuni
Carb Series: BS33
Carb Model ID: 1AA00 (XN models) or 1FL00 (XNC models)
*Main FUEL Jet Size: #100 or #105
**Pilot FUEL Jet Size: #35 or 37.5
Main AIR Jet Size: #120 (non-removable, in carb throat)
Pilot AIR Jet Size: #140
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5FZ82 (all except XNC model)
Main jet NEEDLE ID: #5FZ83 (XNC model)
Main needle JET Size: #Y-2 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3.0mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

 

OK. Now I'm confused. The 1985 maxim 700 is air cooled and has Hitachi carbs. So lm right about that But my 1982 Seca 750 has Mikunis.
I thought. I'm not home right now so I can't go to check. But that parts diagram is definitely my Carb but the diagram doesn't tell who made the carb. I'm going to synch them tonight and see what happens.

 

Your 82 Seca 750, my 82 Seca 750, and all Seca 750's had Hitachi carbs from the factory.
Someone, at some point, swapped carbs for some unknown reason.
The Mikiuni's can be made to work, but you won't be able to use any of the jetting or set-up information from the manuals.

The diagram you linked is for the Hitachi's.

 

Ok there is quite a good chance that I am losing my mind. I don't know why I thought that the bikes had different carbs. I'm home now and I checked my Seca and I can't figure out why I thought it had Mikunis. Maybe I misread it somewhere. Another thing is that mix screw. I see it now but I have no idea how I missed it when I had the carbs on the bench. I'm usually extremely thorough. I'm so picky that I feel like starting over completely as if I was just getting it out of the shed now. I'm posting a picture of "Vern". Before and after so you guys don't think that I'm just some idiot.

 

I found out where I got the dumb idea that Vern had Mikuni carbs. Off of this spec sheet. I was misinformed. Thanks for setting me straight but I should have clued in when both bikes were so alike.

 

Mistakes: it's what people do. It's also how we learn. Mistakes are good.

 

If mistakes are good. I AM AWESOME. . LOLLOL

 

I just might be awesomer.

 

Ok those mixure screws on my bike were all set at 3 and 2/3 out. I'm the only one that's touched that bike. When it was put away 5 years ago it was running excellent with them set that way. Is it not weird that they were like that? And could that be my problem now? And why would it be a problem when it wasn't before?
Also, when I do adjust them, do I complete one at a time or do a minor adjustment on each until it runs perfect

 

could be the o ring is failing or failed replace the o rings set them all to where you found them .
then you adjust them. this is where a color tune plug comes in handy.
other wise you do it by ear
or by temp.
or plug chop

 

Just an update. Right now they are set at 2.5 turns out. If it sits for a bit it will start with the choke/ enrichment valves 2/3 open. It will run like that as long as I don't touch the throttle or the enrichment valve control. If I try to give it throttle it won't rev up. It bogs and usually stalls. It might start up once or twice more than wont start at all until it sits for a while again.

 

Also, What o rings???

 

Ther are some very small o-rings on each idle mixture scres at the nedle end. They seal the passage, preventing an vacuum leak, which will lean the fuel mixture.

3 1/2 turns out may be compensating for dirty passages or a small vacuum leak.
When you say that you are the only person to have touched the mixtur screws, do you mean that you are the person who removed the anti-tamper plugs that block access to the idle mixture screws?

 

When I got the bike years ago. The dealer that I bought it from serviced the carbs. The mechanic that did that work must have removed the limiter caps. They were gone before I got the bike. It ran excellent for a few years and then I didn't drive it for 5 or 6 years. I'm embarrassed to say it wasn't put away properly. Carbs weren't drained, no fuel stabilizer, nothing. Just parked.
So I got it out a few weeks ago, drained the fuel, removed the carbs, changed the spark plugs, changed the oil and filter.
I disassembled and cleaned the carb very very carefully. (FYI. I am a licenced mechanic. Not a motorcycle mechanic, but I have restored about 10 toys like dirt bikes, motorcycles, 4 wheelers. And fixed numerous carb problems for other people. So they were not my first carbs by any means but I've always been intimidated by dual carbs, three carbs and 4 carbs that are together).
So anyway I carefully inspected every orifice , passage and jets. Blew each carb out thoroughly with compressed air, checked the float levels. And reassembled them. For some unknown, foolish, reason I missed all 4 mixture screws.
I put the carbs back on the bike and started it up and took it for a ride. It ran great for about 3 miles and then it guilt and wouldn't start. I let it sit for a minute and then it would start with the choke but then quit if I tried to give it throttle, Then it wouldn't start until I let it sit for a minute. I tried many times and then I got it moving and drove it back home the 3 miles. It sat and idled fine so I shut it off. Tried to start it and it started perfect, without waiting a minute. About 15 minutes later I started it back up went a couple minutes to a store, shut it off, came out of the store, started it up and it ran perfect back home and I parked it.
Still it had a popping sound so I checked the spark plugs and the left outside one was black and the other three were a nice beige. So that's when I first wrote on this forum (I think). So I've had it running well a few times but then it will do that thing where it runs with choke on and not take throttle, and inevitably stalls and won't start up again.
I also checked the synchronization of the carbs and they are perfect according to my tool.
Sorry for being so long winded but this is almost the whole story. Maybe someone will spot a mistake I made. Like the mixture screws before.

 

Those Orings seem to be unavailable as a Yamaha part, because that needle is not suppose to be serviced. (Hence the limiter caps). Does anyone know where to buy them????

 

Chacal@xj4ever can get them for you
These are used in many brands of carbs and I buy them by the bushel from him as I do many sets of carbs every month

 

Hey XJ550H. thanks for posting this stuff about the ignition system. But I've read it a couple times and I'm unclear about it so I haven't done it yet. Would you mind elaborating a bit. Sorry in advance for sounding like an idiot. But I just haven't come across many ignition problems.
Where do I measure the pick up coils, I mean where do I put the ohmmeter leads.
I don't know where to measure on the ignition coils either. You said "input from main wireing harness". But TO where.
And plug wires to where.

 

Yeah. I did find some aftermarket kits. THANK YOU TOOMANYBIKES. I, since I wrote that post took the mixture screws out and took out the o rings. I cleaned out and blew out, with compressed air the mixture passage. I inspected the Orings with a magnifying glass and they actually look like new. (They obviously are not). But just say in'.
It still runs the same.

 

Ok Guys. More info.
It will start after it sits for a bit.
It starts on half choke
Throttle makes it stall
When it's running on 1/2 choke mixture screw being turned in and out does not effect
it's idling.
After it starts back up 2 or 3 times it won't start at all.
In its no starting condition 1 spark plug is wet and black.

My theory, is that my whole problem is that 1 carburetor. My Question to you guys is......... Will one carburetor cause my problems? As I said before, I do have experience with snowmobiles and stuff and I've had twins run on 1 cylinder and triples run on two. But when this bike was running I pulled the plug wire off of the cylinder that's giving me the problem and it quit. As I also said before I don't have any experience with multiple carbs. They intimidate me.

 

How do you do it by temperature? And what is plug chop?

 

One item not mentioned or I missed it ...the fuel line was it kinked in some way...sometimes it could shut off fuel flow but when engine off it refills float bowls. Your bike looks nice. Good luck .

 

Start a conversation with Chacal.

And since the one idle screw has no effect:
Pull the spark plug wire from that cylinder. What happens?

Pull the spark plug, insert it into the wire and ground it to the head. Is there spark?

 

One other place in the carbs that causes problems is this fuel circuit in the bowl. It supplies fuel to this brass tube in first pic

 

plug chop is running motor under load at a selected rpm then hit kill switch and look at the spark plug color.

by temp if you have a cylinder with the paper bag brown spark plug color you measure the exhaust pipe temp and set the other pipes to that temp by adjusting the mixture screws.

 

With a wasted spark ignition system if you pull one plug wire and don't ground it you kill two cylinders - 1 and 4 or 2 and 3.
Edit - this should have been worded if one plug wire is pulled and not grounded, then a risk of damage to the coil secondary is possible. See below postings for further explanation.

At the TCI mating connectors under the left side cover. Pull the connectors to check the ignition coil primary and pick-up coils. Check for corrosion and clean as required if needed.

The black to grey and black to orange on the larger connector are the pick-up coils. They should measure 650 ohms +/-20%

The red/white to orange and red/white to grey on the smaller connector are the ignition coil primaries. They should measure 2.5 ohms +/- 10%. They usually read slightly out of spec on the high side, but should be less than 3 ohms at that point of measurement.

The secondary of the ignition coil is measured at the plug caps. The spark plug caps and the secondary of the ignition coils are fairly common points of failures on these older bikes. Try it first with the caps on so you know if you have issues with the connection at the cap to the plug wire. Cylinders 1 and 4 go together, as do cylinder 2 and 3.

Disconnect the caps from the spark plugs and stick the meter leads up inside so that it touches the metal, one lead in cylinder 1 wire and the other in cylinder 4 wire. They should measure approximately 21K - 11K for the secondary of the coil and 10K for the two caps. Repeat for cylinders 2 and 3.

If you get high numbers on the ignition coil secondary unscrew the plug caps while pulling gently and test individually. The coil secondary should measure approximately 11k ohms, the spark plug caps should measure 5K ohms.



If the caps measure high, some can be repaired by cleaning noted by the slots that allow it to be unscrewed:

 

Well I took the carbs back off of the bike. Cleaned and inspected and blew out every orfice with compressed air, didn't see any problem, put the carbs back on the bike.
And guess what. I turned on the primer, opened the enrichment valves and it started up and ran great, on the centre stand. It's pouring rain, off and on here so couldn't take it for a ride but it is at least it starts well and revs up really well. I just would like to fine tune it. THANKS ALL YOU GUYS FOR YOUR HELP SO FAR.

 

Nope. There is still a ground path through the other plug of the pair. Only the disconnected plug will die.

 

From Ignition Troubleshooting Guide by SQLGuy:

http://www.xjbikes.com/forums/threads/how-to-ignition-troubleshooting.21932/

" To do this, current will need to flow from one end of the high tension (secondary) winding, through the spark plug wire, through the resistor in the plug cap, across the gap of one plug, through the metal of the cylinder head, across the gap of the other plug, through the resistor in that plug's cap, and up the other plug wire."

and return to the other end of the secondary.

The other plug may still fire. I should have stated that as a caution if disconnecting one plug cap and not grounding it that it could potentially damage the coil.

Also from that same post in a reply by Chacal - author unkonwn:

"Now, you raise a very good point about disconnecting one plug. Let's
think about that for a moment: we have introduced a very high resistance in the circuit. Voltage will continue to rise in the coil without any path for escape. Eventually, it rises high enough to exceed the break-down voltage of the insulation within the coil, and the current flows via this new path. In the process, it creates a "channel" or weak point through which the insulation value is reduced."

 

But that isn't how the scondary side of a coil actually works. As long as there is somwehere for the induced current to travel, all of the current will travel down that path. Consider that a single-output coil is wound no differently that a dual-output coil, save for the lack of a second sparkplug wire.

 

Exactly, to have a flow of current from a voltage potential, you must have a complete circuit. Current can't travel down a path unless it has a return to the source. When you remove one spark plug cap, you have opened the circuit. The induced "voltage" in the coil will not produce any current until a complete circuit exists, and thus no spark can occur until that happens. So, if the corresponding plug is sparking with one disconnected, the current path has become one side of the secondary, through the connected spark plug, to ground, through the transformer core, and then through the channel it has created by exceeding the insulation breakdown voltage internal to the coil .

Actually they are wound differently. In the case of the single output coil an autotransformer is incorporated. These employ a 3 wire arrangement where the primary and secondary are electrically connected and share a common ground. With these systems the plugs must connect to chassis ground to produce a spark.With the 4 wire XJ coil, a separate primary and secondary exists, and there is no electrical connection between the primary and secondary. No connection to chassis ground is required for this system to produce a spark, but only a means (the aluminum cylinder head) to electrically join the two corresponding spark plugs.

 

Consider that when one plug fouls or fails it does not prevent the other plug from firing, even though there is no spark at the bad plug.

 

https://www.ngksparkplugs.com/about-ngk/faqs/spark-plug-faqs/what-is-a-fouled-spark-plug

"A spark plug is considered fouled when the insulator nose at the firing tip becomes coated with a foreign substance such as fuel, oil or carbon. This coating makes it easier for the voltage to follow along the insulator nose, leach back down into the metal shell and ground out rather than bridging the gap and firing normally."

So, a fouled plug actually reduces the amount of voltage required. It does not open the circuit, but effectively provides a lower resistance path for the current to flow.

 

Also consider the following:
You are looking at the #1 sparkplug, grounded against the head ( I used an old plug). Its coil-mate (#4) is unplugged, with the vacant plug wire cap well-insulated to prevent it from arcing.



None of what you have written is incorrect (except the part about killing both cylinders), but as a practical matter, when presented with any ground path, electrons will flow. Would I run the engine this way? No. It is however a valid fault diagnosis method that will not cause damage when used as such.


For future readers: Just don't try to unplug both plugs from the same coil without leaving a ground path for the coil secondary. That WILL cause the TCI to be damaged.

 

Video is locked for sign in. But yes I believe it will spark as you are suggesting - just not a good idea.

Yes, I restated that as being more of a caution to prevent possible damage to the secondary of the coil.

And from the Yamaha XJ750RH FSM page 117:

Caution

Do not run the engine without any spark plug cap(s) in place. Due to the high secondary voltage, it is possible to damage the internal insulation of the secondary coil.