Topic: '78F carb sync

[mlinder]

I tend to get pretty anal about carb synch and circuit transition, so I spend a lot of time on it.

[eldar]

I dont worry about it much. this next spring I will but I fuss over the idle mix more!

Matt, you CAN tap the press in mounts to use screw in jets. It is very exacting though and you must be very careful.
We had a long lost member do that on his bike and it seemed to work fine.

[matt365]

Matt, you CAN tap the press in mounts to use screw in jets. It is very exacting though and you must be very careful.
We had a long lost member do that on his bike and it seemed to work fine.

Well, I've got that second set of carbs, I could always give it a shot.  Thanks for the help and the ideas guys.

[eldar]

Go VERY easy on it. Do only a little at a time and keep things very clean.

[TwoTired]

My vote for the stumble problem is either the accel pump is not working to full capacity (especially if it hasn't been operated or attended to in a long while)  and/or the carb sync.

One symptom of  carb sync issues is uneven head pipe temps at idle.

Cheers,

[upperlake04]

 I've read here several times that it take 3 passes to get the carbs clean clean.  My experience too.  Probably a good idea to be sure all passages and orfices are spotless before fine tuning.  Soaking and spraying cleaner and air both ways is a good way to learn the construction details.
  Note there is an internal passageway with a crud trapping hard corner in the slow circuit.

[matt365]

My vote for the stumble problem is either the accel pump is not working to full capacity (especially if it hasn't been operated or attended to in a long while)  and/or the carb sync.

One symptom of  carb sync issues is uneven head pipe temps at idle.

Cheers,

Thanks for the ideas TwoTired.  If the accelerator pump is damaged, is it usually a rip in the rubber?   I've actually got a full set of carbs from a '77F, a 79' 650C, and the current carbs off the '78F. 


when I stuck the mercury gauges on it, they were pretty close to even, so I've been riding it with the stumble since August.  I've just got to get on the throttle a little harder off idle, or else it stumbles pretty good. 

Grabbed some guitar strings off my buddy (he had to change his strings anyways so I'll try and clean the idle jets and see how it goes.  Started snowing here today... about 4'' worth of snow.  Guess I'm winterizing the bike soon, and might as well tear it down and finish my seat.

[matt365]

Thanks for the pictures Upperlake.  Those will be a good reference.

[TwoTired]

Thanks for the ideas TwoTired.  If the accelerator pump is damaged, is it usually a rip in the rubber?   I've actually got a full set of carbs from a '77F, a 79' 650C, and the current carbs off the '78F. 

No. On one the holes in the mickey mouse ear part of the diaphragm were swelled shut.  The four squirt post holes (very tiny) are often clogged or restricted, or the check valve balls (two of them) are stuck or fouled with debris.

Cheers,

[Wayne Meuir]

I have an accelerator pump problem on my 78, I think.
Fresh total rebuild on the carbs, including new accelerator pump and it squirts as it should on all four of the nozzles, BUT, when I whack the throttle open, the arm that acutates the pump moves very slowly as it trys to overcome the resistance from the fuel being pumped(compressed), and the actuating arm does not go all the way to it stop, so I assume I am not getting full response from the accelarator pump.  I cannot find anything in the linkage binding, the arm is free, and if there is no fuel in the carb, it will go to its stop with no problem.
My question is: Is there something wrong somewhere, or is this the way it should work?

I am totally new to this type of carb.

Wayne

[matt365]

Thanks for the ideas TwoTired.  If the accelerator pump is damaged, is it usually a rip in the rubber?   I've actually got a full set of carbs from a '77F, a 79' 650C, and the current carbs off the '78F. 

No. On one the holes in the mickey mouse ear part of the diaphragm were swelled shut.  The four squirt post holes (very tiny) are often clogged or restricted, or the check valve balls (two of them) are stuck or fouled with debris.

Cheers,

Thanks, you guys are a huge help.  I'll check it out when I get the time.  Winter is hitting early this year, so it's off the road for now anyways, so no time like the present

[matt365]

Little tip... don't be a dumbass like my buddy and leave a perfectly good set of carbs in a frozen bucket of water all winter...  Opened them up, and this is what I found.

[eldar]

Those would deliver less than optimal operation!

[matt365]

Big-time understatement for sure!

I think I"m going to clean up this set of carbs, throw in the 116 main jets, and replace the gaskets and see if it fires her up.  I've got to do an engine swap with my buddy tonight too.  His XS650 is blowing smoke pretty bad, and we've got a donor engine to test out. 

Snowing right now in Toronto Ontario...  Well, no time like the off season to start ripping into the bikes.