Learning and troubleshooting '90 750 fuel delivery problem

[wcj]

Sorry if any of these problems have already been covered here.

Here's what's happening...

Problem 1:
Bought the bike "semi" running. The PO let the bike sit for a year without starting, but he was able to get it fired up on PRI but it wouldnt stay running unless the throttle is feathered.

Suspected Cause:
PO didnt have vacuum going to petcock so the carbs were not getting steady fuel.

Corrective Action:
Connected vacuum line from #4 vacuum fitting to petcock.

Results:
Was able to get the bike to run without having to feather the throttle. Ran engine long enough to warm up exhaust pipe at head.


Problem #2:
Cylinder #3 is cold.

Suspected Cause:
Sync fitting is broken off the Diaphragm Cap on #3 causing fuel delivery problem to cylinder.

Corrective Action:
Ordered Diaphragm Cap

Result:
N/A

Problem #3:
Carb #2 appears to leak from bowl drain or lower carb area.

Suspected Cause:
No clue... carbs need to be rebuilt? Defective drain screw? Any suggestion for what else could leak near the bottom of a carb would be great.


Am I on the right course? My goal is to get all 4 cylinders running well enough to keep an idle before I focus on driveability.

Thanks,
Will

[arsenic]

I believe your on the right track. If the bike has been sitting for a long time, then yes, a carb clean/rebuild is a good idea.

[md86]

Sounds like you got the first couple issues under control . Kudos . As to the suspected leak , I'd clean the are well first , then prime it and see . A paper towel will help you see where it's leaking . They'll let you know the INSTANT they get wet .
COuld be a bowl gasket on the outs , or something as simple as a bowl screw or drain not tight enough . In any case , all of these are easy enough to fix .

[wcj]

I decided since #3 was dead until I got a new Diaphragm cap in, I would take it apart to gauge what condition the carbs may be in. Here's what I found.

• Float o-ring torn
• Jet clogged
• Emulsion tube clogged

I think it may be safe to just do a rebuild on the carbs.

BTW, I took pics of the entire tear down in case anyone needed pics on carb rebuilds.

[arsenic]

nice pictures dude. And you seem to know what your doing, or you're at least not afraid to figure it out, awesome dude

[wcj]

Thanks. Those pics are actually 20% the size of the originals. Ive never been afraid to take stuff apart. This is what I did to my vette 2 weeks after I bought it. Though the larger parts of a car makes me much less paranoid.

[Sasquatch]

nice pictures dude. And you seem to know what your doing, or you're at least not afraid to figure it out, awesome dude

+1

Great to see your learning the best way, by doing it!

[arsenic]

Thanks. Those pics are actually 20% the size of the originals. Ive never been afraid to take stuff apart. This is what I did to my vette 2 weeks after I bought it. Though the larger parts of a car makes me much less paranoid.

well, taking stuff apart isn't hard, it's putting it back together that will get you

[wcj]

I disassembled all of the carbs today and found the following.

• Mixture screws were all 4-5 turns out from bottom (wth)
• Pilot plugs on 1,2,4 were all loose
• Pilot plug for #2 was causing the floats to be stuck since it had actually fallen out and was wedged in the floats (could this be why #2 was leaking?)
• Seals for the 2 fuel "T"s were both cracked or splitting

I've pulled #1 and #4 off the rail and left 2 & 3 still connected. This way I have less reassembly when all the seals get here.

Question:
Should I lube the new seals and o-rings with some motor oil when I reassemble everything?

[Sin]

I disassembled all of the carbs today and found the following.

• Mixture screws were all 4-5 turns out from bottom (wth)
• Pilot plugs on 1,2,4 were all loose
• Pilot plug for #2 was causing the floats to be stuck since it had actually fallen out and was wedged in the floats (could this be why #2 was leaking?)
• Seals for the 2 fuel "T"s were both cracked or splitting

I've pulled #1 and #4 off the rail and left 2 & 3 still connected. This way I have less reassembly when all the seals get here.

Question:
Should I lube the new seals and o-rings with some motor oil when I reassemble everything?

answer for number 2 cylinder most likely and the t seals being bad would cause the leak also

[md86]

Question:
Should I lube the new seals and o-rings with some motor oil when I reassemble everything?

Nah , just swipe your finger across your nose or forehead to get some of the grease on your fingertips and rub the new rubber bits . Helps just enough to get them to seat , but not so much they'll slide back out .

[wcj]

Got the carb put back on today and it's alive!

I initially had the carb butterflies set wrong so idle was 5k, but I was able to quickly remedy that.

Also, I made a temp fuel tank for $8 by using a coolant recovery kit I found at Autozone. Works like a charm and holds 1.5qt of fuel.

Sounds like it may need the valves adjusted so Im considering doing that now that I know the bike runs.

[arsenic]

I have a coolant recover tank that I made an aux fuel tank out of, is it made by Summit Racing?

[wcj]

Nah, it's just cheapy Autozone kit.


It has 3 nipples so it worked perfect for the Pre fuel system. 2 were used for fuel delivery and the 3rd acted as a vent.

[arsenic]

I used one of these:

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2DG1474&N=700+400304+115&autoview=sku