Trying to get it back on the road....

[bobinthemtns]

Okay--

The prologue to this post is the "Died on the side of the road!" thread I started last week, while I was... dead on the side of the road and then having to limp across the state, I'm trying to get the puma going again and needed some input.

Here's the issues-

Bike is a '77 R100S and will start, but the left cylinder sputters and backfires constantly, right cylinder runs fine.

After a few minutes the left header starts to glow from the heat- most have diagnosed this as a lean burn condition. But dammit! what is causing it!!

Prior to it dying (that was caused by a loose battery terminal) it was driving fine, but at higher speeds/rpms I could feel a little hesitation and maybe some small backfires. It felt like I had something in the bowls- The sensation started to get worse after about 30-40 miles. I stopped to check, they were fine, but then it just went to hell... it was constantly backfiring when I started it back up....

So far I have:

- Checked the throttle cable and choke cable, both seem fine.
- Adjusted the pilot screw- seemed fine
- Cleaned the bowls multiple times, removed the jets and cleaned them out- all seemed fine
- Checked fuel levels in the bowls, level is fine, gas is available from the lines.
- Checked and adjusted the valves, (the exhaust on the left side was a bit tight, but not much)
- Checked the plugs- right is (obviously fine) left looked fine, but was wet with gas.... is that normal for what seems like it should be a lean burn? I'm guessing it's just from the cylinder running so crappy that not all the gas is getting combusted..?
- Swapped the leads, spark plugs and coils.. no change.
- Swapped the hoses between the carb and head from side to side to check for airleaks, no change.
- Looked in the front cover to see if water/sludge etc had gotten in there- (I did drive thru a rainstorm the day before everything went to hell), but it's been a week of dry weather since then and everything looked fine inside there. I wd40'd all the connections. But it seems to me that if there was a problem with the points/condenser/timing then BOTH cylinders would be outta whack. But the right one is running strong...

Next Steps:

- I'm going to replace my inline fuel filters today, to see if that does anything.. I doubt it because it's getting fuel to at least the right cylinder in appropriate quantities... and the crossover is fine...

- I suppose dissemble the carb... I've already looked at the needles etc.. but could a torn diaphragm cause a lean burn? Not quite sure of what to look for when I'm in there... but maybe something will jump out.. OH- I noticed when I took apart the elbows that gas was getting blown up the elbow towards the airbox.. I guessed that's from the backfires blowing fuel the wrong way- but might that point to anything?

So any help would be greatly, and I mean GREATLY appreciated.

Bob

 

[ISAMEMON]

compression check time. at least that would be my next step. burned intake valve ? just starting to brain storm

 

[69zeff65]

Absolutly a compression check

You may have a valve issue in there, back firing and fuel getting pushed back into the intake tells me you may have either a stuck intake valve or the seat might have come loose and the valve is bent and open. One thing rain or excessive moisture can do is knock carbon loose or the rapid cooling of the head (when big water hits it) can cause the valve seat to fall out. Hopefully if that's happened it only did a little bad stuff.

 

[bobinthemtns]

Okay-- thanks for the beta so far-

I guess I'll go get a compression tester during lunch... any tips on using it would be appreciated.

Regarding checking for a stuck or bent intake valve- does that necessitate removing the head, or is that something that can be done by only removing the head cover? When I adjusted the valves last night- it didn't seem like it was stuck- it would activate back and forth in place... Am I missing something?

And Brewmeister- I was going to go back through the jets and needles tomorrow morning when I was planning on going through that carb. But regarding the timing/advance/cond. etc- wouldn't the right cylinder running good negate those as a possibility?

 

[69zeff65]

A quick check under the valve covers

Quick pull your valve covers off again, take your spark plugs out and turn the motor over slowly and look at the tops of the valves and rockers. You should be able to tell by close observations if something is wrong and a valve is hanging up or sticking. Now a bent valve or loose seat may still move in and out so you really have to look close and maybe even take some sort of measurement of the valve stem. That might give you a hint right away if something bad happened but I would also plan on a compression check as well.
When you do it: fully charged battery, both spark plugs out, properly and safely ground plug wires, throttle will be fully open, do one side at a time and let it turn over about ten revolutions or until the needle on the gauge stops. repeat the test on each side about three times just to be sure about your readings

 

[69zeff65]

Oh yeh

If you do have an obviously bent valve or damaged seat and its confirmed by the compression test (one side will be 115-150lbs and the other a lot lower like in the 20s) you will be pulling the head anyway so you might as well do both sides and get it over with all at once.

 

[20774]

For the compression test, the engine should be warm and the carbs should be removed. At the very least, you will need to prop open the CV carb slides...they won't open just by twisting the throttle.

 

[Troutluck]

It's my understanding that the gasket around the choke mechanism can get sucked into the housing, causing an air leak and a lean condition. I would check that and the choke return springs. Is the choke completely off on the left side in standard running condition?

 

[bikerfish1100]

And Brewmeister- I was going to go back through the jets and needles tomorrow morning when I was planning on going through that carb. But regarding the timing/advance/cond. etc- wouldn't the right cylinder running good negate those as a possibility?

you are correct. If one side runs fine, and the other does not, then you can pretty much rule out any "combined" parts of the fuel/ignition system- points, timing, condensor, fuel quality, tank sludge, air filter, etc.

 

[88bmwjeff]

You might want to try switching carbs (e.g. left to right). I know they're really not designed to run that way, but for short run I think it could be helpful. If the problem switches sides, then you know it's the carb. And, if it doesn't, then you'll know it's not the carb.

 

[crazydrummerdude]

Sounds like my R90. I've done the same as you, and more. Still backfiring. I hope it's not a messed up valve. I am going to swap plugs/coils with my other airhead to rule those out, too.

Doesn't sound like diaphragms. When those tear, the bike runs fine up to 60 miles an hour. Then, no more power. It doesn't backfire, it just bogs down.

When you inevitably take your carb(s) off, check your intake spigot. Sometimes those loosen. Check the rubber hose there, too.

 

[lmo1131]

BUMP

Bob.... you up'n running yet?

 

[bobinthemtns]

Arrrrgggghhhhh!
No! it's still running like hell!

But, put in a LOT of time working on this weekend-

- Checked compression-- it's @ 147 psi in both cylinders (yay for that)

- Bribed a buddy who's an engineer to help yesterday, and we traced every single wire across the whole bike... (sidenote: now I know why I haven't been able to get my brake lights to work!)

But it's still backfiring!

But at this point, it's got to be the carb. We've checked everything else. I'm going to swap the carbs per Jeff's suggestion to make sure- but we've checked everything else...

I partially disassembled the bad carb in question and couldn't find anything that looked out of order... diaphragm looked fine- the one thing I saw was that on the pilot screw and the pilot jet, both o-rings were dry-rotted.. but I would assume that would result in a rich mixture, not lean... but they've been replaced at this point.

Couple of questions regarding the carbs:

- I was running it without the airbox elbows and the carb on the bad side was spitting fuel around in a spray, with a fair amount of it splashing back towards the airbox... But the good side carb didn't seem to spitting fuel around like that.... might this cause any issues?

- When reinstalling the pilot jet, do you screw it all the way in until it seats? Or do you need to back it out a touch like the mixture screw? Ditto for the main jet?

The Bike only has 33,000 miles on it- so I'm guessing that it probably doesn't need the needle replaced..?

Any other thoughts that could be causing issues???

 

[James.A]

I recently solved a problem similar to what you describe by ditching a Dyna ignition and reverting to points. A backfire into the intake side suggests a badly mis-placed, or should I say, mis-timed spark. The Dyna that I tossed was the kind with 2 pick-ups to time each cylinder seperately.

A bent valve will kill compression on that cylinder. I enjoyed an episode of that a few years back. A bent valve will not close off the cyinder and the entire 4 stroke process will be defeated. The cylinder will not fire, it will be dead cold. It won't even draw the air/fuel mixture thru the carb to dump unburned fuel in the exhaust.

A lean mixture will cause the cylinder to super heat, as you've described. Your spark plug would be whitish like new. A lean mixture can be caused by (1) an air leak on the intake side of the head, (2) an obstructed jet or passage in the carburetor, or(3) an inadequate fuel supply to the carburetor, which would make the bike run like you are about to need to switch to reserve.

Great idea about switching sides with the carbs, by the way. All the jets should be seated in their bores, only idle air mixture screw is backed out. It varies from some carbs to others but generally the initial setting is 3/4 to 1 full turn out from bottom.

 

[krpntr]

i had a problem like that once. Took the bike apart trying to find something wrong. Turned out to be coils. I recently read that about 90% of carb problems are electrical.

 

[kentuvman]

+1 Krpntr

Thought poor running was carbs - turned out to be bad plug wires (found that out when saw craked wire near plug cap arching the the dark.

Same applies to bad points & timing. Have a '71 Honda SL125 - was sputtering, ran like crap. New points & setting timing was the RX.

Hope you figure this out! Always interested to learning more.

 

[44006]

assuming that when you looked into front cover at points area you looked closely from the side as engine was turned to confirm that advance assbly and flyweights did not touch (or come close enough to arc) the wire to points or its end fitting and points or points mounting plate has
not come loose

Need to get systematic and absolutely confirm if carbs or ignition or valve issue

1) do switch carbs from side to side - not much work and will absolutely
narrow the problem to ignition or carbs - do not bother to hook up choke wire
just see that lever is pushed all way down to stop peg - do not put on air tubes
so you can see that the slides rise with vacuum as rpm increases

1a) if problem switches side with carbs then first check the choke assbly
for gasket problem or adjust on wire not pushing lever all way to bottom

2a) if problem stays on same side with carb switch then switch spark plugs
from left to right - if problem changes sides then fault is spark plugs

2b) if problem still on same side then switch spark wire connections from
left to right without disconnecting anything but the plug caps from plugs -if problem changes sides with wire switch then problem is spark wire or a coil

report back here

IF RUNNING WITH AIR TUBES OFF AND BACKFIRING - RUN ONLY OUTSIDE AND
BE PREPARED TO DEAL WITH POTENTIAL FIRE

IF problem still stays same side after all this then intake valve closing is somehow
intermittent (sticking probably at rpm but not at compression test speed) - or
lifter sticking?? It is hard to believe valve seat drop problem if compression test was so good and even

 

[lmo1131]

Just throwing this out...

It rained here two nights ago ... really unusual for central California, in September, and it was a heavy down pour for about an hour and a half. The /5 was parked in the driveway with it's cover on... the one that covers everything but the cylinders... it's usually parked in the garage, but hey, I got home late, and it never rains here in September.. .

The bike was very hard to start the next morning and ran intermittently all the way down to the shop, about three miles. Bursts of power, heavy intermittent, missing, another burst of power... totally unpredictable performance. It had run perfectly the night before.

I had resurrected the left cylinder 5Ω spark plug cap a week earlier when it pulled apart as I pulled the cap off of the spark plug ... lots of corrosion in it as a result of moisture getting past the rubber boot where the plug wire enters the cap... I cleaned up all the parts and reassembled the cap... it ran great until the rain the other night.

So I knew exactly where to look ... I replaced the OEM metal-jacketed Beru style cap with (as recommended by others here) a new 90?? NGK LB05F spark plug cap ... runs like a champ again. And all for $2.69

I know things may look okay, but sometimes they're not. I chased a problem with my wife's misfiring Karman Ghia for about a week after a complete tune-up using all new parts - turned out to be a defective spark plug which, under load climbing a steep hill near the house, would misfire. On the straight and level... no problems at all.

 

[pandry1]

Timing Problem

I bought a 1977 R100 several years back - same type of problem. Just riding it home, my left shoe got so hot it changed several shades darker than my right shoe - it felt like my foot was getting fried!

I looked at everything and finally found the spark advance mechinism on the end of the cam shaft was not working properly (the weights were sticking) - and - the cam shaft was bent causing the entire advance mechanism to wobble. With the front cover removed, you could see it jumping up and down with every revolution -(it turns at half the speed of the crank). These problems were causing distortion of the timing on the left cylinder. I cleaned and adjusted the points, replaced the condenser for good measure and cleaned the advance mechanism. I then carefully tapped on the cam shaft (ahhhhh) until it was straight and no more wobble. Careful - remember to protect the threads and take your time - if you screw this up, it requires a total teardown and a new camshaft.

It's fairly easy to determine if this is problem. Get out (or borrow from your local VW mechanic) an old fashion strobe timing light and hook it up to one cylinder, then the other. They should both fire at the same mark on the flywheel at idle and at speed. Also, the firing position should move smoothly as engine speed increases / decreases and remain in the same position for each cylinder at a constant rpm.

Anyway, this corrected the problem - bike ran great/cool the whole time I owned it.

 

[stanley83]

I recently solved a problem similar to what you describe by ditching a Dyna ignition and reverting to points. A backfire into the intake side suggests a badly mis-placed, or should I say, mis-timed spark. The Dyna that I tossed was the kind with 2 pick-ups to time each cylinder seperately.

+1

I had a similar problem on my R75/6, kept loosing the left cylinder, initially after the bike warmed up, then all the time. Pulled the Dyna III and reinstalled the points, along with a Dyna points amplifier. I chose this method because if the amp. dies on the road, it can easily be pulled from the circuit and the bike will run on points as originally designed.