Back for more help *eye roll*

[JonathanPD812]

...I wouldn't think a float level within a millimeter would cause this problem....to be plainer: possibly because the ignition is failing while the gas is continually being sucked in.... or less likely something else like fuel supply failing...

Some of you guys have now mentioned my ignition system or specifically the ignition coil and I have been talking to a buddy of mine who is really into model a Fords and he said in his experience this sounds like an ignition coil issue where it runs fine until it heats up.

I feel like I can eliminate a fuel supply issue as well because I have disassembled, and rebuilt the petcock and it operates as it should, but also as a worst case scenario it operates just fine on the prime setting ensuring optimal flow of fuel to the carburetor and as you mentioned above if my float height is close in theory I should be getting good fuel through the carburetor.

I guess the next thing I have to check would be my ignition system but that I am not familiar with at all. I'll break out the clymers manual and take a look, but where would you recommend I begin when troubleshooting the ignition system / ignition coil

[Gorminrider]

I'd start with replacing the condenser, checking the points and the centrifigal advance mechanism (behind the points plate is it?) thereafter, i'd run the bike until it stops and check the spark at the plugs exactly then while still hot... You may need new coils but check everything else that's fixable and cheaper (including wire harness, connections, spark plug caps and KILL switch) first. rare things too, like chafe or cracked rubber on hi-tension leads...

I'd recommend you get familiar with how ignition works- it's a very common system you have especially with "points" as your bike came with? It surely does not need yet another explanation where the internet has so many...AND You can learn from manuals of other bikes of the same vintage that have exactly the same system-POINTS-it's very common-it's NOT "cdi" so look away from anything about that...

[JonathanPD812]

I'd start with replacing the condenser, checking the points and the centrifugal advance mechanism (behind the points plate is it?) thereafter, i'd run the bike until it stops and check the spark at the plugs exactly then while still hot... You may need new coils but check everything else that's fixable and cheaper (including wire harness, connections, spark plug caps and KILL switch) first. rare things too, like chafe or cracked rubber on hi-tension leads...

I'd recommend you get familiar with how ignition works- it's a very common system you have especially with "points" as your bike came with? It surely does not need yet another explanation where the internet has so many...AND You can learn from manuals of other bikes of the same vintage that have exactly the same system-POINTS-it's very common-it's NOT "cdi" so look away from anything about that...

Thanks for the list of things to check! I will speak to some things I tried below:

I have checked the points (both old ones and new ones I have) and confirmed those are good, and my gaps have been set properly.

The advance mechanism appears to work fine (not sure how to check it other than make sure it moves freely?).

The plug shows signs of definite carbon foaling. A soft black sooty deposit that can easily be wiped off.

I have thoroughly checked the wire harness and it is flawless.

I had an issue with a kill switch in the past and it has been replaced and double checked after replacement.

I am going to buy some new condensers, I found some online reasonably priced. Based on the above, it appears I am inching closer to the problem. Thank you all so far! I will comment once again when the condensers arrive.

[Gorminrider]

yes, no rust and free motion is Pretty ok on the advance unless you have a strobe light...it's just something to bear in mind as part of the system as your issue doesn't seem to be timing...
If it is the coils, in the last resort, at least you will have a good chance they won't go bad again with every thing else in good nick...or maybe they've just aged out or previously abused.
Do be sure it's them-you might even find similar used ones from a generic any-brand motorcycle to put in-don't be fixated on "Suzuki" because all this stuff is really from "nippon-Denso" or the like. The mounts to fit them in the space IS important though. be sure of that, Suzuki or not. Pictures online can be unreliable...
If you can, buy decent condensers...Modern ignition doesn't use them anymore and the cheapos can be pretty badly constructed so maybe something from Bosch? for a vintage BMW? would be a good bet...if it fits in the space any condensor should do.

Internet BMW Riders - Substitutes for BMW Parts

[JonathanPD812]

Okay I'm back, finally got around to this once more and I'm stumped again. New condensers installed, out everything else back together aaaaaaand... Nothing. Well to be specific it starts just runs very rough... Doesn't idle, needs the have the throttle open about half way to stay running but is only at like 2000-3000 RPMs... Idk what to try next...

[Gorminrider]

O gee what a drag...sooty plugs are usually considered to be overrich air-fuel -that said, it's really pretty common on old bikes diagnosed in a shop while idling a lot...a long run is what these "plug diagnosis" refer to and it's assumed the bike is running ok , so the fix is offered to use a hotter plug. But do check you are running good, correct plugs of course.... It might be you are missing sparks (sigh)
... running rough all the time is the bad one- DO check all the cylinders are firing. Often bad lowspeed is a missing cylinder-you can tell easily by starting the cold bike and checking the warmth of pipes.....needn't say don't burn yourself. If it's missing cylinders, that's a big clue. If it's missing a pair, that's a clue.

if it's all cylinders bad, you'll have togo through the tings common to all cylinders or pairs of them in 4 cylinder bikes...
you'll have to go back through the basics and check them off. "fuel,compression,spark " - fuel supply, carbs or even "out there" as the charging regulator has failed(check for voltage at the battery being above 14.8 and "jerky"-that'd be AC voltage which won't run the bike at low speed and is very jerky-headlight will also flare as revved)......

[JonathanPD812]

O gee what a drag...sooty plugs are usually considered to be overrich air-fuel -that said, it's really pretty common on old bikes diagnosed in a shop while idling a lot...a long run is what these "plug diagnosis" refer to and it's assumed the bike is running ok , so the fix is offered to use a hotter plug. But do check you are running good, correct plugs of course.... It might be you are missing sparks (sigh)
... running rough all the time is the bad one- DO check all the cylinders are firing. Often bad lowspeed is a missing cylinder-you can tell easily by starting the cold bike and checking the warmth of pipes.....needn't say don't burn yourself. If it's missing cylinders, that's a big clue. If it's missing a pair, that's a clue.

if it's all cylinders bad, you'll have togo through the tings common to all cylinders or pairs of them in 4 cylinder bikes...
you'll have to go back through the basics and check them off. "fuel,compression,spark " - fuel supply, carbs or even "out there" as the charging regulator has failed(check for voltage at the battery being above 14.8 and "jerky"-that'd be AC voltage which won't run the bike at low speed and is very jerky-headlight will also flare as revved)......

Thanks for the to do list! I will go through the following:
* Check plugs / replace as needed
* Check cylinders (both firing)
* Voltage check
* Compression check
* Spark check
* Fuel check

I will post back when I cross all the things off!

[Gorminrider]

I just finished reassembling with a float height at 26.2 on each side,

I know the spec sheet posted says this but it's notably a lot more than my gsx400 or any other bike on the sheet....not saying it's wrong but it reminds me per your issue.
On my bike, This would make very lean running and my bike wouldn't even idle. Perhaps you have brass floats that are heavy? But whatever, do check that the bowl gasket is off when measuring and that BOTH carbs are correct.If one is a fair amount different, on a twin, you won't get the bike to idle on both cylinders...

Your specific symptom does encourage doing this...ie:no idling. If your idlemix screws are having no effect, again, beyond cleaning,(see the recent thread https://www.thegsresources.com/_foru...pilot-jet-plug specifically there's a tiny passage between main and idle wells....) the float height could do it.

[JonathanPD812]

I know the spec sheet posted says this but it's notably a lot more than my gsx400 or any other bike on the sheet....not saying it's wrong but it reminds me per your issue.
On my bike, This would make very lean running and my bike wouldn't even idle. Perhaps you have brass floats that are heavy? But whatever, do check that the bowl gasket is off when measuring and that BOTH carbs are correct.If one is a fair amount different, on a twin, you won't get the bike to idle on both cylinders...

Your specific symptom does encourage doing this...ie:no idling. If your idlemix screws are having no effect, again, beyond cleaning,(see the recent thread https://www.thegsresources.com/_foru...pilot-jet-plug specifically there's a tiny passage between main and idle wells....) the float height could do it.

This is very interesting. I do have the brass bowls in my carbs. I plan on taking the carbs off tonight and I will look closely at those plug on the pilot jet as well as my float height.

[Gorminrider]

it's the little passage between main and idle "wells" that is super important...(I think later mikunis got rid of it and the plugs)If you look at the manual's diagrams it's very informative...and with carbs out you can blow throw the idle passages from the airbox side : You have to pull the main jet needle and idlemix screw out, plugging all the various holes with your fingertips except one...until you can actually hear a tiny bit of air at the last tiny hole under the idlemix screw where the idle mix enters the intake...On old carbs, I wouldn't expect both the be exactly the same at that little hole but air should go through nearly the same. a 1/2 turn of the idlemix should take care of any difference.

Brass floats would explain the higher float spec, so follow the specs (read the manual- but usually, bowl gasket must be removed to measure.) Probably brass is harder to shape as efficiently as the plastic ones and so are heavier per the airspace they contain... DO shake them in case they are leaking with fuel inside.

[JonathanPD812]

it's the little passage between main and idle "wells" that is super important...(I think later mikunis got rid of it and the plugs)If you look at the manual's diagrams it's very informative...and with carbs out you can blow throw the idle passages from the airbox side : You have to pull the main jet needle and idlemix screw out, plugging all the various holes with your fingertips except one...until you can actually hear a tiny bit of air at the last tiny hole under the idlemix screw where the idle mix enters the intake...On old carbs, I wouldn't expect both the be exactly the same at that little hole but air should go through nearly the same. a 1/2 turn of the idlemix should take care of any difference.

Brass floats would explain the higher float spec, so follow the specs (read the manual- but usually, bowl gasket must be removed to measure.) Probably brass is harder to shape as efficiently as the plastic ones and so are heavier per the airspace they contain... DO shake them in case they are leaking with fuel inside.

I have the carbs removed and cleaned them thoroughly. Using canned air I tried what you mentioned above with success. I'm glad you mentioned the plugs not being a thing in later carbs because in mine they are not. I think the last thing to do before putting the carbs on the bike would be to verify the float height. As opposed to getting terrible particular on float height, should I instead ensure they are the same and check the height using the clear tube on the drain plug trick? What is the ideal level below the seam of the bowl if I go that route.. The carb rebuild guide does not say, but the picture shows something in the range of 2.75 mm below the seam if I remember correctly...

[JonathanPD812]

I just wanted to update before anyone else posts, it may help you.. and me. Carbs are clean, I blasted cleaner through each passage with success. I forgot about the cart on BikeCliffs site so i went back to that, set my float to 26mm from the surface without the gasket, and tried the tube method to verify float height. The chart states. 6.5 mm below the gasket surface and I am right on the money. I feel very good that the carb is clean and set correctly.


Next I will verify my plugs and my point gaps. If all is good I will reinstall the carbs and fire her up. Hopefully it starts right up and runs well so I can verify both cylinders are firing and then check voltages at different points and finish with a vacuum sync. I'm assuming if I get that far, then all will be will from that point forward and I'll be back on the road. STAY TUNED.

[JonathanPD812]

Alright .. all back together ... Fires up, I can't get it to idle (let it idle no issues for 10 minutes) when I touch the throttle it boggs down... If I slam on it and get past 4k RPMs then it work... I can ride it if I keep it over 4k but otherwise it stutters and dies. Plugs always look black and sooty. I tried moving the needle clip as a last ditch effort and it won't even start on anything other than the 3rd position.

I have verified my gaps, voltages, float height / fuel level, compression, I have good fuel flow, and have the filter in the tank nice and clean and installed an in line filter because my tank was pretty rusty... I used evaporust to clean my tank and that worked well but in the past I had rust chips in my carb so I installed the second filter...

I'm totally stumped why it won't just work... I still feel like it's got to be an issue with my carbs but I don't know what to do because I haven't changed anything performance wise and it ran great before I let my brother ride it so I haven't changed any jets or anything but I'm thinking i may need too?

Is it possible that it worked before because it was tuned to work with some failing condensers and points and cracked intake tubes and now that I've fixed those things I need to re-jet?

[JonathanPD812]

Typo* at the beginning I said I can't get it to idle and I actually can and let it idle for 10 mins*

[Gorminrider]

The problem is your brother. You must kick him really hard in the shins and ask just what the heck he did to your bike! Put diesel in it?
Generally, it's the simple thing nobody bothers to mention. Also common is in the neighbourhood of the last thing done to the bike before trouble. (your brother...time for the cattle prod and the hard wooden chair!)

Have you read the concurring thread about "advance mechanism springs" ?(https://www.thegsresources.com/_foru...ronic-ignition)
Did you read UKjules thread per his 250? turned out to be a ground. https://www.thegsresources.com/_foru...ways-and-stops
When ideas run out I've had to go and sit in the garden for long periods until some new idea occurs and I can return to the fray hope rekindled...! unfortunately it can take a few of these until The One pops in.
- Is the Choke/Enricher functioning? Is it pulling both the shafts of the choke pistons in and out?
-Have you ever tried riding it with the petcock on prime? (The float needles should have no trouble holding back without the vacuum mechanism in play.)
-The fuel filter shouldn't bother it -but if your tank filter is ok I'm not sure what it does beyond adding clamps to the fuel line and many people distrust them.
-Is it possible the airbox rubber collar is folded a bit and blocking the idle mix intake jets?
Does one exhaust pipe get hotter sooner than the other when starting? (I mentioned that previously)