3k Stumble

[spectra]

New to the 1100s and just picked this one up a few weeks ago. I knew having a few smaller XS models that they have carb issues if not cleaned. So I ordered new boots as the factory ones were shot and someone put RTV on one. Also 4 rebuild kits and also front and rear brake kits. All these parts are K&L as I read a post of someone recommending them. Well rebuilt the carbs and one hell of a time trying to get it to run.......found another post saying the K&L stuff was junk so........dug through a box of stuff that came with the bike as somewhere along the way a 4 into 1 was put on it and someone replaced jets and messed everything up. Found some mikuni jets that were factory so replaced everything I could with the mikuni stuff. Bike fired right up and idled ok. Synced the carbs and have it running great but there is a slight hesitation at 3 to 4 K ?

Last night took it out and same thing. Give it throttle and it starts to fall on its face ? Found out if I pull the choke out one position it runs really well ? I understand I may have the wrong jets as it has the exhaust but it seems to run good. Its a little rich but that's ok with me. I think mixture screws are 2 turns out.

Any help appreciated! Thanks!

[HalfCentury]

New to the 1100s and just picked this one up a few weeks ago. I knew having a few smaller XS models that they have carb issues if not cleaned. So I ordered new boots as the factory ones were shot and someone put RTV on one. Also 4 rebuild kits and also front and rear brake kits. All these parts are K&L as I read a post of someone recommending them. Well rebuilt the carbs and one hell of a time trying to get it to run.......found another post saying the K&L stuff was junk so........dug through a box of stuff that came with the bike as somewhere along the way a 4 into 1 was put on it and someone replaced jets and messed everything up. Found some mikuni jets that were factory so replaced everything I could with the mikuni stuff. Bike fired right up and idled ok. Synced the carbs and have it running great but there is a slight hesitation at 3 to 4 K ?

Last night took it out and same thing. Give it throttle and it starts to fall on its face ? Found out if I pull the choke out one position it runs really well ? I understand I may have the wrong jets as it has the exhaust but it seems to run good. Its a little rich but that's ok with me. I think mixture screws are 2 turns out.

Any help appreciated! Thanks!

How did you determine that it is running rich? Did you perform plug chops?

I am less than an expert, but if you have a less resistive than stock exhaust, I would think that the bike would have a tendency to run lean.

Did you take out every jet and probe all the holes in the carb bodies? Did you probe all the holes in the jets and emulsion tube?

Did you do a compression test of all cylinders?
Did you check all the valve clearances?
Did you perform a carb sync?

A stumble at low RPMs makes me think of of valve clearances, carb cleaning and carb sync.

[natemoen]

Doing a good and proper sync you will never end up with tge idle mix screws evenly turned out. Every cylinder will be different.

Let us know which type of carbs you have and what jets are in it.

[spectra]

No plug chop was performed. I am no expert but the plugs just looked rich to me. I do know one of he PO had messed with all the jets and I have a bunch of jets that came with it. I just put it back to factory specs to get a starting point.

All carbs were totally pulled apart and all jets were cleaned and yes a couple were pretty dirty.

Compression is 140 to 150 on all cylinders.

Carbs were synced with a vacuum gauge but by me and I am no expert.

I was messing with it last night and it is getting better so I am not sure if I just didn't let the bike warm up enough or ? Idle was a little low so I bumped it up and now seems a lot better on throttle response.

Jets are 137.5 on the mains and 42.5 on the pilots.

No valve check that is on my list of to dos.......I do know the cam chain tensioner drips a little oil. I am reading up on changing that out.

[HalfCentury]

No plug chop was performed. I am no expert but the plugs just looked rich to me. I do know one of he PO had messed with all the jets and I have a bunch of jets that came with it. I just put it back to factory specs to get a starting point.

All carbs were totally pulled apart and all jets were cleaned and yes a couple were pretty dirty.

Compression is 140 to 150 on all cylinders.

Carbs were synced with a vacuum gauge but by me and I am no expert.

I was messing with it last night and it is getting better so I am not sure if I just didn't let the bike warm up enough or ? Idle was a little low so I bumped it up and now seems a lot better on throttle response.

Jets are 137.5 on the mains and 42.5 on the pilots.

No valve check that is on my list of to dos.......I do know the cam chain tensioner drips a little oil. I am reading up on changing that out.

If the valve clearances are out of spec, you will be chasing your tail with carbs, plugs, synching.

[spectra]

If the valve clearances are out of spec, you will be chasing your tail with carbs, plugs, synching.

Yep I am new to these and learning. I just knew the carbs were really dirty so started there.

I am reading up on valves and also looking in my manual. A lot of good posts on here but now that all the pics are gone that stinks. I am a picture person

Thanks for the help!

[natemoen]

Did your carbs have a screw over the pilot jet?

[spectra]

Did your carbs have a screw over the pilot jet?

Yes they had the brass screw over them.

[natemoen]

Yes they had the brass screw over them.

Not being nitpicky, just want to be sure. It's usually an aluminum screw so I just want to make sure you aren't thinking about the brass main jet in the tall tower are you?

The pilot is in the shorter tower and is completely sealed off from the bowl (no hole in the screw) and then has a smaller long jet buried down in the tower.

I am asking these question to make sure that the carbs are early model carbs. If you had late model carbs on there the jetting is completely different.

[spectra]

Not being nitpicky, just want to be sure. It's usually an aluminum screw so I just want to make sure you aren't thinking about the brass main jet in the tall tower are you?

The pilot is in the shorter tower and is completely sealed off from the bowl (no hole in the screw) and then has a smaller long jet buried down in the tower.

I am asking these question to make sure that the carbs are early model carbs. If you had late model carbs on there the jetting is completely different.

Yes the screw with no hole. Mine looked like brass but who knows. On my smaller 400 there are no screws just rubber plugs over the pilot jets.

And yes the shorter tower as the mains were taller.

So just pulled the valve cover off to check valves what does everyone use for a new gasket? Old one is toast it was so brittle so don't even want to attempt it.

[BA80]

Every 78 79 engine I've had there was that little hiccup between 3 and 4K.

After that little hiccup there's a huge power surge. I personally think it's because of the duration (length of time the valves are held open) in the grind of the early cams. Kinda boggy at low end but when it hits that RPM range it kicks it.

I've tried tuning it out endlessly but it just winds up taking from one end and giving to the other.

The later engines ( 81 - 83) don't have that issue due to a shorter duration, higher lift cam grind. The valves open wider but don't stay open as long. Smoother power but nowhere near the kick of the early engines.

Just my observation from experience.

[natemoen]

Yes the screw with no hole. Mine looked like brass but who knows. On my smaller 400 there are no screws just rubber plugs over the pilot jets.

And yes the shorter tower as the mains were taller.

Yeah, the rubber plugs are part of the change over to the later model of the carbs.

Ok so we know you have early model carbs and jetting is correct for them as a baseline. Now we need the valves checked/ adjusted.

[spectra]

Every 78 79 engine I've had there was that little hiccup between 3 and 4K.

After that little hiccup there's a huge power surge. I personally think it's because of the duration (length of time the valves are held open) in the grind of the early cams. Kinda boggy at low end but when it hits that RPM range it kicks it.

I've tried tuning it out endlessly but it just winds up taking from one end and giving to the other.

The later engines ( 81 - 83) don't have that issue due to a shorter duration, higher lift cam grind. The valves open wider but don't stay open as long. Smoother power but nowhere near the kick of the early engines.

Just my observation from experience.

Thanks for the heads up. Yes it has just a slight hiccup and then comes on hard.

Going to check valve clearance now and go from there. Need to get some gasket maker first though......

[spectra]

Yeah, the rubber plugs are part of the change over to the later model of the carbs.

Ok so we know you have early model carbs and jetting is correct for them as a baseline. Now we need the valves checked/ adjusted.

Working on that now but may just wait for tomorrow night......All fluids were drained and fresh was added today along with a filter. Adjusted the cam tensioner and now its the valves. But if out of spec will need shims so I am sure that will be mail order.........

[spectra]

Ok said screw it and pulled out the feeler gauge.......so intake side is pretty good everything at or under .18mm now the exhaust side well that's where the issue lies.........had one cylinder at .28 the rest were .23 to .24 still in spec but the high side according to the manual. So now I guess I need to get some shims and a tool. Where is the best place for that ? not sure my local shop has it but will check in the morning.