Help! '82 GS450T No Start - Has Spark! Weird Mismatched Carb?!?

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New member here - joined for some community expertise...

Model: 1982 GS450 T

Issue: Won't start (has spark)

Symptoms:
-has spark (big & blue)
-turns over
-130lbs compression (cold)
-batt voltage: charged 12.8, in bike 12.5-12.8, key on 12.0-12.1, cranking 10.8, after trying a while 11.5-11.6
-battery is a Bike Master BB10L-A2
-sometimes backfires through right exhaust

Already:
-cleaned, reoiled air filter
-cleaned out carbs, reset float height (more on this in a sec)
-new plugs
-drained old gas, refilled w/ fresh 87
-checked petcock operation (fine)
-confirmed gas in float bowl
-tried starting with starter fluid through airbox - doesn't stumble or come to life for a bit (about a 1 sec spray's worth)
-signal generator checked out ok w/ multimeter
-kill switch, clutch switch, and ignition switch seem to be working fine

HERE'S THE WEIRD PART:
The carburetor is definitely a Mikuni 34mm but it doesn't match this bike. The fuel screws are visible from the sides (older style???), and the float height absolutely cannot be set to 23mm. The float will bottom out on the top of the float bowl before it gets there.

I set the float to the ~26mm that is said in my Clymer for "all other models" and it still wont start. It was set at about 27mm with the springed shaft on the fuel inlet needle compressed under the weight of the float. I reset it to 26mm (like i said) with the springed shaft extended - while holding the carb at a 45 degree angle.

What model is this carb from? (no real markings, an "A" on the float bowl) Will it work?

How do I verify gas into the cylinders?

*Also: Could a bad CDI still spark? Could anything else mess up the timing of the spark?

Thanks everyone!

I'll try to have pics of the carb up asap!

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Pics as promised...

[mpencegs]

Grab a fire extinguisher and an eye dropper. Remove the carbs and place a very small amount of gas in one of the chambers. If it fires then yes its just simply that fuel is not getting into the chamber. If not then its something else.. Also you need to check and adjust your valves.. Also you can try reseting your air/fuel mix screw. turn it in slowly and note how many turns it takes to feel it lightly seat. Set to to 2 turns out or if the original setting is close then back to those settings.

Suck on the vacuum tube on the fuel tank and confirm fuel flow when set to ON.
Grab a rag and losen the fuel bowel bolt and verify that you have fuel..

Pull the plugs and see if they are wet to confirm that fuel is entering the chamber.

I kinda threw all my ideas out there. I have some trouble with my carbs as well..

[mpencegs]

Yeah that pic they look exactly like my cabs on my 81 gs450 TX.. The haynes manual from bikecliffs website for the 450 will give you the exact number for that make of carb.

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I have the carbs apart (again) ... there's a "K" on the carb body inside the carb bowl. Does this ID it any better? There are no other markings.

Per the Clymer manual on BC's website...

"The correct float level for all models is
25.6-27.6 mm (1.01-1.14 in.). The
correct float level for GS450 models is

21.4-23.4 mm (0.84-0.92 in.)."

Again, 22-23mm is not happening... I'll see if I can get a pic...

Thanks again for the help!

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For further reference:
-pilot jet = 17.5
-main jet = 115

*when the carbs were off I took an eyedropper and put some gas on the intake side... didn't do much popped/puffed a bit - but didn't run or stumble... for this test should I have put the gas directly in the cylinder via the plug hole?


Thanks

[pete]

They look just like mine on my '82 450E, they look exactly right.

Forget the float height level in the Clymer, the correct height is 26.6mm +/- 1mm. This is from the factory manual. Clymer are talking about the earlier 400 and 425 carbs I'm pretty sure.

Next up, when you say you cleaned out the carbs, exactly how did you clean them? If they've been sitting for any period of time you will need to strip and dip them, as in 24 hours or so in good proper carb cleaner. Refer to Flaming Chainsaws' 450 carb rebuild guide on BassCliff's site for details.

You will also need to get yourself an excellent O ring kit from www.cycleorings.com if you haven't done so already.

Next up, your pilot and mains are stock sizes, nothing wrong there.

Have you tried with the choke on? I assume yes but don't see it in your original list...

And, as mentioned earlier, valve adjustments are quite important. Hard starting is a symptom of poorly adjusted valve clearances.

Oh, and having the mixture screws exposed simply means someone has already removed the caps.

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Thanks for the correct float level pete... going to set it now...

check, check, and check regarding dipping, o-rings, choke - haven't touched or checked the valves yet.

What is a good starting point for the 'pilot air screw' (mixture screw)?

Do I go with the book's 1.25 turns out? or 2 full turns out?

Thanks again everyone!

[pete]

Hmmm... I'd be starting 2 or 2 1/2 turns out...

[Steve]

What is a good starting point for the 'pilot air screw' (mixture screw)?

First of all, get the terminology correct.

That is the "idle mixture adjustment screw". It is not the "pilot air screw" or the "fuel screw" mentioned in your first post.

Personally, I start with them running rich, after I rebuild a set of carbs. I will start with them three full turns out from lightly seated. The slightly richer mixture is like having a partial "choke" setting, and assures that the bike will start easier when cold. When the bike is warmed up, turn them in slowly, listening for the point when the idle speed starts to drop a bit. When you hear that, back up about 1/8 turn, go to the other cylinder, repeat.


Back on the "terminology" topic:

Could a bad CDI still spark?

Yes, it could, but since you don't have a "CDI" on your bike, I wouldn't worry about it.

What you are trying to call a "CDI" is actually called the "Ignitor", which is actually a bit of a mis-nomer. It doesn't really do any igniting.
That box is just a set of transistorized 'points' that control the flow of electricity through the coils. When the 'points' (transistors) open, the coils make the spark.

There are two channels in the ignitor (one for each cylinder), it is possible for just one of them to fail.

.

[Mekanix]

Are your plug wires backwards ?

Putting a little gas in the plug holes will usually cause it to start or kick a few times if it has good compression, correct valve and ignition timing.

Backfiring like this is usually due to incorrect ignition timing or really low compression or wrong valve timing.

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Thanks Steve for setting me straight on the terminology. I was just using what the book "said" and what others have online. Clearing it up helps understand the functionality.

Mekanix-
If the compression is good, and so is the ignition timing... how does bad valve timing keep it from starting? Thx.

I'll be testing some gas in the plug holes after I set the float height.


Additionally,

How far in should the "throttle adjuster" screw (clymers words lol) be?? Would having it out and the throttle valves closed all the way keep it from starting? Should there be an initial 'gap' around the valve to get air flow/vac?

Thanks again and again everyone.

[Mekanix]

Slightly open, usually I would set it and give a little throttle while cranking it and when it started I would keep it running by hand and then set the idle.


If your sure its firing on the compression stroke on the cylinder its supposed to, then valve timing can throw things off by allowing the intake or exhaust valve to open or close too soon or late.


Did you have the cam tensioner out recently or done anything to the engine?



Don't use start spray. It will wash the cylinders down of oil.

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I didn't. But there's a cam tensioner in the "box-o-parts" and one installed on the bike. So yes, or the PO was planning to.

I'm sitting down, what could possibly be wrong?

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Gas in the plug hole made it pop and bubble a bit... maybe slight backfire too right side

didn't really sound like it was shuddering or trying to start.

black/w coil on right side
white coil on left

...each coil lead goes to the cylinder on the corresponding side. Also, the wiring plugs are keyed so no mixups there.