86 750 Carb Trouble - Page 2 - Suzuki GSX-R Motorcycle Forums Gixxer.com
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post #21 of 24 (permalink) Old 06-26-2019, 05:19 PM Thread Starter
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Join Date: May 2019
Posts: 39
Re: 86 750 Carb Trouble

We're talking about Mikuni jets.

I swapped out the 150s for 152.5 jets and something went COMPLETELY awry. Now it's only running on a couple of the carbs. I have another thread about it here:

I don't want to cross-post like crazy, so let me know which thread would be better for this.

After investigating today, I found the following:

Compression test results:
Carbs Off:
1: 145
2: 140
3: 125
4: 150

Carbs On, Idle:
1: 60
2: 90
3: 120
4: 140

Carbs On, WOT:
1: 125
2: /
3: /
4: 150

Temps at the exhaust headers:
1: 196
2: 390
3: 510
4: 600

I cleaned the crap out of the pilot jets and had zero luck.

Pictures of the carbs attached here:

Photo 1 is a weird thing I noticed with the spring for the sync. Seems like it isn't causing issues, and trying to remove it was causing way more trouble, and the spring is already buggered into the position it's in.

Let me know any other pictures I can send, or any other stats. I'm completely at a loss at this point.
cratcliff is offline  
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post #22 of 24 (permalink) Old 07-08-2019, 04:58 AM
Join Date: Mar 2019
Posts: 10
Re: 86 750 Carb Trouble

Whats with the bar thing in the spring???

It looks stuffed you need to replace them I doubt you'd be able to balance them in that condition

If they are too far out of sink which it looks like, that could cause the WOT problem to high a main jet will also cause WOT problems.

I would replace the spring/s make sure butterflies are all opening as they should, check diaphragms have no tears, jet needle and jet not tooo worn, Bench sink the carbs, set to factory on the pilot screw drop back the main to @ 145 and start again after a good clean inside out
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post #23 of 24 (permalink) Old 08-01-2019, 10:16 AM Thread Starter
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Posts: 39
Re: 86 750 Carb Trouble

Sorry to bump a pretty dead post. Took the bike in to a shop and they found a few key things wrong:
1) 2 of the carbs had missing / damaged retainer rings on the needles
2) carbs were quite out of sync

They resolved those issues, which got the carbs back in good tune. Bike idles great, runs great at low RPM etc. Now the only thing left to resolve is the WOT issue. They love the bike (guy who was working on it actually built this exact bike up back in the 80s), and spent quite a lot of extra time on it for me, trying to track it down. The things they did, along with the results:
1) Compression test - all results were above 160 and all about 160
2) leakdown test - less than 10% loss
3) checked all electronics
4) completely checked through carbs
4) jetted up and ran on dyno
5) jetted down and ran on dyno

Per the mechanic, it sounds like it's dropping 2 carbs at WOT (probably 3/4 -> WOT).

Next steps as far as I can tell are to check the valves, and probably pop the carbs off and check all of the values for the pilot air jet etc. I'm not sure what all they have changed over time (I know that it ran great consistently with the current setup).

If you guys have any advice I would greatly appreciate it!
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post #24 of 24 (permalink) Old 08-02-2019, 09:42 AM Thread Starter
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Re: 86 750 Carb Trouble

Bump! Honestly have no idea what could cause all that WOT trouble that already hasn't been checked out
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