Engine poping

[lunut87]

Well it's been a while since I've been around.

but...


I have a confusing(to me at this point) problem going on with the good old 79 XS1100F.

I guess I should give the run down on what the bike has done to it and what I have done to try and solve my issue.

First off. It is basically stock. Stock air box, stock carbs, stock everything except for the exhaust system. It has a Jardine Equal length tube header 4 into 2 with crossover pipe exhaust system. As far as I know the carbs have never been jetted. I spoke with the previous owner, who put the system on the bike and actually owned the bike from brand new, and he never re-jetted, and said he never had a problem, but for all I know he never ran the bike with the system.

Now the bike was sitting in a barn partially dismantled for about 15-16 years. last year I went through the revival process. Cleaned carbs, dumped all the fluids...yadda yadda. I wound up having to replace the TCI unit to actually make it run. The bike seems to run really well. I had to replace the timing advance diaphragm because it had a vacuum leak. Everything in that department seems to be working now.

I have just this week, re-cleaned the carbs, completely took apart, and soaked in a carb bucket, each one over night minus rubber seals of coarse. I also pulled the intakes and they seemed a little sketchy so I coated the insides with a nice coat of black silicon sealer to stop any vacuum leaks in that area. Also, as per my dads thinking, I ran a compression test to check for and sticky valves. It was consistent across all cylinders, +/- 5 PSI of each other across the board. Didn't seem to find anything that way so I pulled the valve cover to inspect the valves. There is plenty of oil in the top of the head, and not a spec of rust. I cranked over the engine and watched the valves and didn't notice any lagging behind the cam lobes.

I have been riding the bike. Seems to have a lot of power but it has slight burps under heavy load. If I try and wind her up through a gear it seems to all of a sudden pick up and then drop back off almost instantly. (I thought this problem would be solved by the vacuum advance, but doesn't seem to have changed.) Now i'm at a loss for where to go next.

From my experience with engines, it seems like the timing is advanced causing a popping, i don't know how or even if the timing can be adjusted. Sometimes it pops through the carbs and sometimes into the exhaust, pretty random in that aspect, but it is consistent at a certain RPM. 2500-3000 it pops on acceleration and it pretty much always pops when engine braking, if I pull the clutch it stops popping and drops back to idle. I have checked the inductive pickups. wiggled the wires with the bike running and cannot make it miss a beat...I have opened the TCI unit that the bike is running on and the solder joints appear to be good, nice shiny looking, and plus the bike runs on it.

I'm pretty stumped at this point. Kinda thinking about possibly jetting the carbs, but have no way of knowing how to do that, or if it's even the next step. The other thing I was thinking about is possibly replacing the coils, since I'm running on stock coils.(what should I replace them with, if I should?)

Sorry for the giant post, but I wanted to give a full overview of the situation.

[TopCatGr58]

Hey there LUNUT,

Welcome, congrats, now let's get to work!

Okay, you say you soaked the carbs minus the rubber seals, yet you don't know how to rejet?? I hope you are not talking about the large rubber diaphragms on the tops of the vacuum slides as the rubber seals??
The Seals we have warned about damaging when soaking the carb bodies are the ones around the butterfly shaft seals, one on each end of the shaft. To have removed them, you would have had to grind off or otherwise unping the ends of the small screws that hold the butterfly valves onto the shafts to remove them, then the shafts, as well as separating the carb bodies from each other! But I'm thinking that if you don't know how to REJET a carb, then I don't think you would have gone to this much trouble to remove the shaft seals! I could be wrong!? But this could be one problem, that you have damaged the shaft seals causing vacuum leaks.

Secondly, just wiggling the PickUp Coil wires won't necessarily reveal a break, you need to give them a decent TUG. See the repairs tech tips for info on this, nice photos as well!!

Back to the carbs, again NO ASPERSIONs to your skills intended, but we've heard lots of oopses around here! You say you took the carbs completely apart. There are screw caps over the pilot jet towers, and then the pilot jets down inside there, and that circuit can easily get clogged/gummed up. Also, aside from the Main Jet, there is the emulsion tube that slides UP thru the carb body from the main jet side, has lots of small aeration holes that also easily clog!

Have you checked the Pilot Jet/IDLE screws tips to ensure that they are intact, that no tips have been broken off?? What size are the main jets? Their size is stamped on the head of the jet, may need a magnifying glass to see it!

The PO may not have used NEW Exhaust gaskets/o-rings when installing the pipes, leaks there can cause popping as well.

On the coils, plug wires, have you removed the plug caps from the wires, checked for corrosion, cilpped off 1/4" from end of wire, reattached plug caps? ALso, what do plugs look like, bleach white, or sooty black, somewhere in between?

Let us know, and we'll continue! T.C.

[oseaghdha]

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If I try and wind her up through a gear it seems to all of a sudden pick up and then drop back off almost instantly.
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That sounds like a slipping clutch.
You are likely dealing with more than one problem.

[DiverRay]

TC wrote:

There are screw caps over the pilot jet towers, and then the pilot jets down inside there, and that circuit can easily get clogged/gummed up.

Sorry, TC, but this is a '79, NO COVERS!! Just a plastic cap on the screw.
Lunut,
The "popping" as you slow down is usually a leak in the exhaust. Check the bolts at the header to head connection. If you don't know how bad the gaskets are, I would replace them.
The hesitation MAY be the pick-up coil wires TC was talking about. The '79 is old, and they have been flexing for a while! Read the tech tips, and plan on about one hour replacing the wires. I use test leads from Radio Shack, as they are made to flex, and are easier to find than the original "high flex" wire. Just do ONE WIRE AT A TIME so you don't mix them up!
Replacement coils can be had from mikesxs.com. I think they are back ordered on the $35 coil, but they have a $69 coil that WILL work once you bypass the ballast resistor.(an easy job, just unplug and plug the left over wire into itself)

[TopCatGr58]

TC wrote:
Sorry, TC, but this is a '79, NO COVERS!! Just a plastic cap on the screw.

Hey Ray,

I was talking about the pilot jets tower inside the float bowl, not the pilot jet SCREWS. Depending on his familiarity with carbs, seeing a SCREW HEAD over the pilot jet tower, he might have thought that it was a screw that held the carb body together or something, and not that it was just a cap screw to seal the tower, so that it would draw it's fuel from the main jet tower via the tunnel. This little description was for HIS benefit, I know YOU know this!

Enjoy that second cup of coffee now!
T.C.

[lunut87]

sorry for the delay, life is busy right now. I haven't done much to the bike as of yet. I guess when I said I didn't know how to rejet it was more so the sizing of the jets for my application rather then the actual physical jetting of the carbs. I will have to remove the carbs again to look at the jet sizes, so it might be a while before I can post those.

I did remove the butterfly valve from the shaft and removed the throttle shaft seals that you are speaking of. I did NOT soak the diaphragms attached to the needles. The small jet wayyyyyyy down inside the carb was removed and soaked out side of the carb along with all the jets I could remove without grinding or drilling. I also removed the brass center section of the carbs and soaked those separate, this being the passage that the main jet needle rides in. I don't feel that there is a vacuum leak in the actual carbs themselves. and again I did coat the intakes with a nice coating of silicone and let it cure before installing the carbs back on the bike.

I will check over the exhaust system, before this last time of cleaning the carbs it did seem to be back firing through the carbs and not just the exhaust. Since the clean I have not messed with it or ran it long enough to see if that had stopped, but that issue is normally a timing thing in my experience.

I guess I need to be more aggressive in my wiggling on those pickups to make sure they are really good, but I will do that too. Just to be sure. There isn't something that could make the TCI unit cause a timing issue is there?

now as for the idle air screws at the front of the carbs, closest to the engine, mine have plastic caps on them, I did remove them for cleaning. This time I noticed that two of them were broken off in the carb, I don't know how to get them out. So my solution to the problem was to just close all of them. I was under the understanding that they are just idle air screws and were not super important, they just allowed air around the butterfly valve. Maybe this is my issue? How many turns out are they supposed to be set at?

I have another set of carbs that were originally on the bike, but they were so messed up and the screws were so corroded that i couldn't get them apart. My dad had another complete '78 or '79 engine around and I stole the carbs of that engine and are using them for my bike.

Would it be a bad thing to grab the #2 and #3 carbs from the original set and use them with my current #1 and #4 carbs that I am running with now? I would need to verify that all the jetting is the same, but my dad was saying something about them being matched as a set. but I never really understood his concern. This would solve my broken idle air screw problem.

[petejw]

Hi Lunut,

Yep, those mixture screws need to be replaced and the tips
removed, there are a few posts on here that show different tecniques to remove them.

The idle mixture screws a very important and actually work through out the rev range,
they meter fuel not air, the air pilot jet is located at the rear of the carb.

Realisticly the bike shouldnt idle, but when you do replace them start with
1 half turns out as a starting point.

Be real careful when screwing them in, they break off real easy.

[Dragon Tamer]

Lunut,
My thinking here is that your problem is caused by the broken pilot screw tips. Get them out and replace the screws and check it out because the way you are running it will cause a "lean" condition and this WILL cause it to pop.
Also for your information, the Jardine "spahgetti" exhaust system does tend to pop and burble on deceleration/engine braking. This appears to be a normal characteristic of the system. However is should NOT do so on acceleration.
If you check the two spark plugs on the two cylinders with the broken screws compared to the other two I am sure that you will see a difference in them. Make sure that you get all of the springs, washers and o-rings back in the correct order on the pilot screws when you replace them or they will not work properly either!

[lunut87]

that makes a lot of sense. I was under a false impression with those screws then. It makes sense that they are lean, I have noticed the chrome on the head pipes turning a bit orange like they are getting hotter then they should be. The Jardine system is a nice enough system that I don't think it should be dis-coloring as bad as it is under normal conditions.

Right now I do have them all closed and I noticed the idle is a little funny, . Sounds like it has a cam with some valve overlap in it. Probably that lean condition if that is indeed my problem.

I'll search up that removal technique and see where it gets me.

Is there normally a jetting adjustment required for the Jardine "spaghetti" system?

[petejw]

yep the bike will run like crap throughout the rev range with them all
screwed in.

Get the mixture screws repaired and adjusted correctly, take the bike for a good ride before thinking of rejetting. If your running the stock airbox
and filter you should be sweet with the stock jetting.

[Dragon Tamer]

The Dragon is running the stock jets and the stock air box. The pilot jets are @ approximatley 2-3/4 turns out YMMV as all engines vary a little. Like Pete just put it, get the screws repaired/replaced and run it for a while to see what it might want from there.

[lunut87]

perfect will do. I'll post results when I get it all sorted out.