Topic: Am I correct in my thinking??

[splittie]

The bike: 1975 CB750
The problem: Seems to be running a little on the rich side
The question: When I went to make adjustments at the air/fuel mixture screw, the #2 and #4 carbs made no difference when making an adjustment. The #1 and #3 would make the bike start to die back if the screw was tightened too far. I thought it a bit odd so I went to the sparkplug and pulled #2 and #4 plug wires individually and there was no change in the idle speed of the bike. Plug wires #1 and #3 would make the bike start to die when pulled.
All of the head pipes are hot (although it is a 4into1 header soo the heat may be transfering) and when the plug wires are pulled, you can hear the spark hitting.
The only thing I have not done yet is a compression check.
Any suggestions on the cause of this?

[eurban]

Impaired idle circuits in the 2 & 4 carbs.

[splittie]

Impaired idle circuits in the 2 & 4 carbs.

OK I'm a newb, what are and where are the idle circuits ?
I would assume you are talking about the idle jets, correct?

[masonryman]

your slow jets or the passages to them are most likely blocked if the cyl's come in once your off of idol

Mark

[splittie]

your slow jets or the passages to them are most likely blocked if the cyl's come in once your off of idol

Mark

So, if I run it at higher than idle and pull a plug wire it should make a noticable difference?

[masonryman]

assuming you are getting gas, that is, it is only the slow jets that are clogged...

Old bikes and their carbs can be fickle.

mark

[splittie]

Well that bites, I just rebuilt all 4 carbs.

[masonryman]

no ever responds when I say this but I will one more time.

I always soak the carbs I work on in "the Works" toilet bowl cleaner and use a syringe to inject it in all the passages, air and gas, rinse with water and blow all passages with compressed air till the carbs are dry. They should be bleached out from the acid in the cleaner and make sure you can see light through all the jets, the holes are very small, some don't even know you should be able to see through them.

Mark

[splittie]

When I rebuilt, I put all new jets in also, so if they are plugged, I guess it must have happened since the carb work.

[masonryman]

That could be my first 550 I had the carbs off 8 or 10 times before I was happy with them. get some in line filters and change them often till you are sure the tank is clean

[masonryman]

 FYI cyl 1&3 and 2&4 are on the same coil and are fired by the same trigger, don't over look the coil and points

[BIKE]

no ever responds when I say this but I will one more time.

I think I know why.

[jsaab2748]

FYI cyl 1&3 and 2&4 are on the same coil and are fired by the same trigger, don't over look the coil and points

 isn't it 1-4 and 2-3 on the same coils?

[masonryman]

no ever responds when I say this but I will one more time.

I think I know why.

I know, I know, But when you are a poor boy playing with junk you will find a way

[masonryman]

FYI cyl 1&3 and 2&4 are on the same coil and are fired by the same trigger, don't over look the coil and points

 isn't it 1-4 and 2-3 on the same coils?

I think you are right I have a set of pipe's that are 1 in to 3 and 2 in to 4

[splittie]

FYI cyl 1&3 and 2&4 are on the same coil and are fired by the same trigger, don't over look the coil and points

New set of Dyna coils and plug wires, so there should be no problem there.
I ran the bike up in rpms and pulled the #4 plug wire and noticed a difference in how it ran, so It looks as if its the idle jets.

[masonryman]

A little bit of crud goes a long way when it comes to screwing up the operation your carbs

[splittie]

Hey masonryman,
This is tottaly off the subject, but I live right up the road from you!
Well kinda  there's a city of Selma located just a few miles away from me here in California.
OK, well I thought it was funny.
cya

[KingCustomCycles.com]

1-4 and 2-3 same coils.  Points plate is marked that way also.  Put in new points AND condensors, time it correctly, and clean those carbs like it was your last day on earth.  She will run fine. 

To give you some idea of how common this is, I keep 5 sets of points and condensors and 4 cans of carb cleaner in the shop at all times. 

[martino1972]

and valve clearance??