Carb Help!!

[Haarstad]

I have a 79 XS1100 Special with 78 carbs on it with cheap pods, and 4-1 kerker exhaust.

I feel like I'm chasing my tail here No matter what I do, I still have the same problem and I've been working on this bike just about every day for at least the last 3 weeks trying a couple different things every day and putting the carbs back to where it ran best before quitting for the day. I don't know what to do next...

My bike won't allow me to go past 5k-6k rpm (or 70-80 mph in 5th gear) and i can't go past 3/4 throttle or the engine cuts out...

I've taken the carbs apart a thousand times to clean everything up and i have tried every main jet from 137.5-147.5 with 140's making it run the best (topping out at about 78 mph). If i go with a smaller jet, i can't get past 70 and if i go any bigger, i can't get past 70...

I have checked the floats and they are all set to proper the proper stock height. I have checked over the diaphragms on the pistons or slides (i don't remember the name) and they are all in perfect condition with no cracks and the carbs don't leak at all.

I have read some pretty bad things about the cheap pods so today i took a dremel and sanded off that lip on the pod boots that get in the way but it didn't make any difference.

My fuel/air mixture screw are set so when the bike is idling below 1k rpm, and i quick twist the throttle, it goes right back to the same idle spot. (It doesn't bog down or stay high for any amount of time... I don't know how else to explain this) My mixture screws are set about 3 turns out.

I have green Mikes XS coils on the bike that were put on at the end of last year, and before the bike was stored for the winter, we checked the valve clearance and all of them had proper clearance. Cause i read that could be a problem.

When i take the carbs off after just running the bike, there is a little bit of fuel on the inside of the carb boots, not much at all but there is some and i don't remember that from last year... However, i didn't have my carbs off this much so i could've easily missed it... I was just wondering if this was indication that it is still rich or if this is normal and means nothing. When i say that there is little there, i mean there is VERY little... I'd say about the minimum amount of fuel that it takes to start to pool up.

I've spent too much money on jets and i don't want to purchase any that are smaller than 137.5 when it seems like it's running the best on 140's... I don't know why it would need to be smaller than stock anyways.

I don't remember if I'm missing anything else but if you have any questions, just ask and I'll let you know. I've tried a bunch of things and I just don't know what to do next Any help is appreciated


Edit: Also, the bike does not cut out when sitting there and i just rev it past 5k rpm. It is only when the bike is under load that i have this problem.

[natemoen]

Did it run well last year before putting it in storage for winter?

[foreda]

Carbs

May not be the carbs if jetting does not help matters. Did you check your exhaust system for a possible restriction? Also, what about compression and are you synchronizing the carbs, correct needle jet setting? Just throwing some ideas out there.
Dale

[TADracer]

Sounds like it could be a weak spark to me. Mikes green coils are 3.3 ohms, correct? If that is correct then you must bypass your ballast resistor or you will not get a very high secondary voltage buildup in the coils. Have you bypassed the resistor?

BTW, before I changed carbs my setup was jmuch like yours and I settled in on 142.5 main jets and 42.5 pilot jets.

[natemoen]

Yup, mikes green coils are 3 ohm and the ballast resistor needs to be removed.

[JustAddHP]

I had a similar issue with one of the ones I have been working on. There is a tiny hole in the bottom of the float bowls that goes in to the drilled hole where the brass tube of the carb goes in to. 3 of the 4 of mine were plugged and it took a while with needles, carb cleaner and wire drills to get them cleaned out. Other than that, I'm assuming all the diaphrgms are good?

[bikerphil]

I had a similar problem, turned out to be a frozen mechanical timing advance.

[Haarstad]

My brother did the green coils. How would I be able to tell it that resistor is bypassed? And yes is ran fine before putting it away last year besides a spuratic idle. Which is why I replaced the carbs and the bike runs amazing except for this one issue. I'll go out and check for that hole in the bowls of the carb and do I need to check the timing advance while warm?

And yes, I have been syncing the carbs about three times during this process, it hasn't really changed

And what are those brass tubes in the bowls of the carbs? What do they do?

[motoman]

I had a similar problem, turned out to be a frozen mechanical timing advance.

Might wanna double read what Phil states here. A common overlooked issue. Remove the vacuum can and then rotate that advance back and forth. should be 'floppy' loose when working correctly.

[dpotter58]

I'll be the one to say check your pick up wires... I ahd the same issue a few years ago. Randy fixed them and no more problems.

[James England]

Fuel cap vent

Have you checked that the fuel filler cap vent isn't blocked? It's a common problem. It has a small hole and gauze/foam filter (tiny) and it allows gas to flow out of the tank by allowing air in. In warm/hot weather, it allows for fuel vapour expansion and lets it out. Basically, it allows the tank to 'breathe'

If this vent is partially blocked, you may find that's why the bike will rev to 5,000 but, when under load, dies. The engine could be drinking the fuel faster than it can fill the float bowls (when under load but not when stationary), so you effectively run out of gas, even though might have a tankful!

There is a great thread on the forum about how to remove the vent assembly and clean it. I found mine was making a strange hiss after a run. I posted here about it and got the answer above. When I cleaned it, it was almost totally choked with flaky, crusty stuff...presumably something in the fuel. It sloshes up into the vent when the bike's bouncing along and then evaporates, gradually leaving more and more deposit.

[jwhughes3]

james is right

I had a similar gas starved situation show up on a XS400 - ran with cap open and problem solved - rebuilt the cap as permanent solution.

Check it first since its so easy to do.

John

[motoman]

I'll be the one to say check your pick up wires... I ahd the same issue a few years ago. Randy fixed them and no more problems.

That was next dpotter, since he would have the cover off anyways......

[motoman]

Have you checked that the fuel filler cap vent isn't blocked? It's a common problem. It has a small hole and gauze/foam filter (tiny) and it allows gas to flow out of the tank by allowing air in. In warm/hot weather, it allows for fuel vapour expansion and lets it out. Basically, it allows the tank to 'breathe'

If this vent is partially blocked, you may find that's why the bike will rev to 5,000 but, when under load, dies. The engine could be drinking the fuel faster than it can fill the float bowls (when under load but not when stationary), so you effectively run out of gas, even though might have a tankful!

There is a great thread on the forum about how to remove the vent assembly and clean it. I found mine was making a strange hiss after a run. I posted here about it and got the answer above. When I cleaned it, it was almost totally choked with flaky, crusty stuff...presumably something in the fuel. It sloshes up into the vent when the bike's bouncing along and then evaporates, gradually leaving more and more deposit.

Actually your location is the cause James. With having a 6percent humidity here majority of the time, mine still looks new under there after 30+ years. Here in the States, those residing east, west, or southern coastal areas have issues electrical, etc. that we never see where I live. For example, the electrical wiring and harness on my Venturer looks like it did the day I bought it. Did replace the fuse panel way back when that was first suggested as the holder tangs were britle and one broke and I re-soldered for a temp. fix.

[James England]

Actually your location is the cause James. With having a 6percent humidity here majority of the time, mine still looks new under there after 30+ years. Here in the States, those residing east, west, or southern coastal areas have issues electrical, etc. that we never see where I live. For example, the electrical wiring and harness on my Venturer looks like it did the day I bought it. Did replace the fuse panel way back when that was first suggested as the holder tangs were britle and one broke and I re-soldered for a temp. fix.

Yes, there was also rust under the fuel cap and that didn't help. The UK is renowned for its rain huh? It's June and it's been raining for about 3 weeks. The forecast says rain throughout the entire of June. That's a first!