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Discussion Starter · #1 ·
I bought my daughter a 1980 kz250-D (LTD) for her first bike. Cute bike and perfect for her. Ran good but only to 45mph. I found a tear in the CV diaphragm, so patched it up with G glue.(Keihin cv32) Now suddenly runs super rich with even 10% throttle, but idles fine. Any throttle will almost choke out the engine. I went back and defeated the diaphragm by taking corner off, still rich - no change. Reset bowl level extra low - no change. I checked spark at plug boot and installed new plug - no change. Advanced and retarded timing - No change. Compression = 115 psi. Cleaned/ Cleaned/ recleaned the carb, jets, air jets, needle jet, blah blah blah - no change.
What the heck happened to this bike to cause a sudden change?
NOTE: previous owner removed half of air box to install the wrong size battery...thanks buddy. It ran fine without airbox before diaphragm repair, but still runs uber-rich even with secondary jet plugged and diaphragm off. Since no change in airbox I suspect that is not the problem.
1) What the heck could cause a super rich condition all of a sudden?
2) Is aftermarket carb an option?

Any ideas 馃挕?
 

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Wow. How did you manage to make the font so small? A bit hard to read for us old fellas... LOL.

A good starting point would be to replace the diaphragm with a new one. One source (no affiliation) is
 

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Discussion Starter · #3 ·
Thanks that's a lot cheaper than OEM. I don't think the diaphragm is the problem. While my repair was kinda backwoodsy, it worked when tested. I even plugged the secondary jet completely, to confirm it is not the source of the excess fuel. I've cleaned and blown out every inch of the carb. I have read the shop manual 10 times and studied parts to all the jets to ensure proper assembly. Still so rich it dies under moderate throttle. What about trying an aftermarket carburetor?
 

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I think aftermarket carbs are very much a hit and miss with mostly a miss. Personally I have not had first-hand experience, but have heard others complain, mainly when they buy offshore carbs.

I am not knocking your repair, and it may be airtight but the repair may have altered the stiffness and balance of the diaphragm. All of these things could impair the rate and amount that it will raise the slide which in turn could explain it running rich. It seems you have eliminated most other possible sources of the problem.

Think about it. In your own words you say in ran fine up to 45 MPH, and then AFTER the diaphragm repair it suddenly ran super rich. To me it says the repair is the problem.
 

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Discussion Starter · #6 ·
Well you were right...I think. I replaced the carb with a cheap aftermarket carb and now it runs great. The carb was a wee bit too tall so it's wedged against the frame, but not bad for $35.
I'm still going to put a new diaphragm in the factory carb this winter just to see how that works.
 
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