Topic: 3/4-full throttle: sputtering and VERY low power

[Spanner 1]

Max, before you take the carbs off check this, remove the airbox or pods (ugh!) and twist the throttle while looking into carb throats....should be an obvious good sized squirt of fuel visible from each little brass 'post' ......must be present to accelerate bike above idle or bike just dies....also pump works at higher throttle openings, so bike would feel 'flat' trying to accelerate on the road.

[BlackMax]

Max, before you take the carbs off check this, remove the airbox or pods (ugh!) and twist the throttle while looking into carb throats....should be an obvious good sized squirt of fuel visible from each little brass 'post' ......must be present to accelerate bike above idle or bike just dies....also pump works at higher throttle openings, so bike would feel 'flat' trying to accelerate on the road.

Well, I yanked the pods off #1 and #4.  I looked as far in as I could, which is difficult,  and cracked the throttle.  I did this 10x and don't think I ever noticed the jets of fuel from the pump.   

But here's a question for you-  wouldn't the accel. pump only affect the initial opening of the throttle....by compensating for the instant increase in air, with an instant increase in fuel?  In other words, if I were to gradually get into the throttle, on the road....wouldn't the accel. pump be out of the picture?   I'll go back out and keep fiddling with it, but I'm sure there is a problem with the accel. pumps.  I just wonder if there aren't other issues, after the pumps? 

Ideas?

[mmtsquid]

Carbs are from
If the plugs are sooty and black, you have a rich condition.
If you have pods, chances are your air intake isn't the problem.
I'm willing to bet the main jets are the wrong size.
Unscrew a float bowl (either 1 or 4) and remove the main jet.
Does it have numbers written on it?
If so, what #?

I'm not sure what size jet is stock for your bike, but whatever that size is i would order that jet and the size up from it.

[mlinder]

These aren't the stock carbs?
Second, no carbs will allow wanking them open to WOT from anywhere below about 3/4 throttle 'cept for CV carbs, whetehr they have an accel pump or not.

Your bike won't go above 3500 rpm with load. This has nothing to do with accel pumps.
Again, my guess is you are only firing on 2 cylinders (for whatever reason, carbs, or ignition), or your advance is not working.

[BlackMax]

These aren't the stock carbs?
Second, no carbs will allow wanking them open to WOT from anywhere below about 3/4 throttle 'cept for CV carbs, whetehr they have an accel pump or not.

Your bike won't go above 3500 rpm with load. This has nothing to do with accel pumps.
Again, my guess is you are only firing on 2 cylinders (for whatever reason, carbs, or ignition), or your advance is not working.

My other bike has no problem, even when cold, from idle to WOT....but it's a modern bike '05 KLR650.  

Carb ID:  well, my mechanic (yea, the one who "tuned it to perfection, lol) said it's off an automatic.  He said there is a vacuum hose that isn't used, so he plugged it.  This carb is also being operated with ONE THROTTLE CABLE only.    On the right side of the carb, the following is inscribed "42A"   followed by an "A" in a box   "QD7"       Does this ID the carb?

Also, the motor is '78 SS (black)

[mlinder]

KLR650 uses a CV carb, like I said, the throttle cable doesn't actuate the slide piston in a CV carb. Vacuum does.
Your carbs are not CV. You cannot whack them open, ever. It won't work. Can't ever. The ability to whack open the throttle on that bike has nothing at to do with it being 'modern'. The carb design is still 30 years old on it. It's just 30 year old CV, as opposed to 30 year old mechanical.

I can't remember the different models of carbs for each bike, but I think 42A was on the F models. Maybe the K7 and K8, too?

One throttle cable is fine, long as the mechanism is working properly and opening all 4 carbs at the same time to the same degree.

[BlackMax]

KLR650 uses a CV carb, like I said, the throttle cable doesn't actuate the slide piston in a CV carb. Vacuum does.
Your carbs are not CV. You cannot whack them open, ever. It won't work. Can't ever. The ability to whack open the throttle on that bike has nothing at to do with it being 'modern'. The carb design is still 30 years old on it. It's just 30 year old CV, as opposed to 30 year old mechanical.

I can't remember the different models of carbs for each bike, but I think 42A was on the F models. Maybe the K7 and K8, too?

One throttle cable is fine, long as the mechanism is working properly and opening all 4 carbs at the same time to the same degree.

Well, I'm going out and ride the thing to determine EXACTLY what it's doing, not doing, and when it's doing/not doing it.   Maybe that will clarify it a bit more.   Stay tuned.

[mlinder]

Did we determine if all 4 are firing?

[BlackMax]

Did we determine if all 4 are firing?

Man, you may have been dead on!  I sort of discounted the "all 4 firing" thing.  But,  just went out to ride it......it won't even idle on 4.  It's now idling on EXACTLY2.  Not intermittent, but constantly and smoothly on 2.  I tried reving, warming it up, etc.  It never even sputtered on the other 2.    I hate this bike.   $4,000 so far and it doesn't even begin to run.

#1: not firing
#2: firing
#3: firing
#4: not firing

I'll get new coils, since the points are new.  I'm getting frustrated beyond words.

[mlinder]

Don't buy new coils yet.

Search for coil testing here on the forum, by twotired. You can systematically check WHY 1 and 4 aren't firing.
I'd write it all down again here, but Lloyd did such a good job already, and I'd forget something for sure.

First things first, though, check for spark on 1 and 4. I do this the masochistic way. I let it run and grab the spark plug boot... if I get shocked, then I know at least I'm getting spark down to the plug. Whether the plug itself is firing is another matter. Get int eh garage or some shade and watch for spark with the plug attached to the plug wire.
If you have spark, then it's a carb issue. If you don't, it's an electrical issue. Again, follow Lloyds instructions for tracking down the electrical issue.
Another quick thing to do is to swap wires on the coils, then swap plug wires. See if 1 and 4 fire now instead of 2 and 3.

[BlackMax]

No spark on 1 or 4.  

I'm too lazy to screw with it anymore.  I'll buying a new coil.  It's the only thing that isn't new or wasn't serviced by 2 different mechanics.  I have to believe it's the most likely candidate.  

We'll see.

One last question:  since it's possible that the guy who put new points in did it wrong,  would it make sense for the engine to falter under load, or have 2 cylinders cut out under load, due to points?  I always thought this is more a classic bad coil symptom.   It doesn't matter that much, as I'm taking the coil to be tested right now.   The guy quoted me $150 for a new set of upgraded coils.  Is that a bit high??

[mlinder]

Well, thats' about the right price for a set of new dynas, plug wires, and boots.
Assuming it comes with plug wires and boots, yeah, that's a good price.

If the points aren't doing what they are supposed to do, you won't get firing, or will get bad firing, on one or both of the coils.
Sorry, I can't remember everything you've checked so far. Did you, in fact, check your points?

[BlackMax]

Had the coils tested....they are perfect.    Dejected, I came back to the house and solved the problem!!

UPDATE......I really spent some time polishing the breaker contacts.  Then, I pulled the plugs and spent even more time with some emery paper between the gap, and a little more time on the insulator.  

Then, I hit the starter and it fired up.  Only now, instead of idling at 1200, it was at 2000.   Hmmmmm, perhaps all the cylinders were actually firing now?  Took it for a quick ride and it seems pretty solid.  Maybe a couple of slightly dead spots, but no big deal.  It pulled to 6k fairly smoothly.  Certainly a 95% improvement.   I'm grinning from ear to ear.

So, my guess is that the points were dirty all along, and this was allowing 1 and 4 plugs to get really fouled up.  There wasn't enough spark to light 1 and 4 under load.  Eventually, both cylinders simply stopped altogether.  I think I've got it  

[mlinder]

OK, so, either the coil for 1 and 4 are either getting a crappy signal of when and how to spark, or your 1 and 4 carbs aren't working properly.
When you unscrew the drain screw from the bottom of the bowl, does fuel pour out?

Also, do as I suggest earlier. Change the leads from points to coils, then change spark plug wires from 1 and 4 to 2 and 3, and vice versa.
If 1 and 4 still don't fire when you do this, you KNOW its a fuel and air delivery issue.

[PxTx]

Were your condensors changed when they did the points?  I had a bad condensor flake out on me above 3/4 throttle.  Hind sight made it obvious as one of them was discolored, but it took me a little while to figure it out.

[BlackMax]

Yea, after cleaning the points and plugs really well, it now runs on all cylinders and even pulls pretty well (not sure if it's 100% since I have nothing to compare to) when I get into the throttle. 

The plugs fouled themselves out.  The question then is, WHY?  Was it the points not sending the right spark?  If so, problem solved.   Was it #1 and #4 carb with blocked air bleeds?  If so, problem will soon return.   Was it too cold a plug (I'm running NGK D8EA)?  I don't think so....?

Anyone running hotter plugs?

[Peters1983]

emery is WAY to rough for points. I have had the same problem with my 750. I am going through some trial an error with my carbs, you may need a few different jets to toy with and mess with the clip settings on the needles with pod filters.

The only throttle response that I ran across was way too lean and the clips run right in the middle. I am running aftermarket pipes and uni filters.

One good test on carbs with an accelerator pump was to leave fuel in the bowls and use a screw driver to move the throttle linkage. the squirters should shoot straight down the intake port( I found on mine the squirters were Way off(they turned in the carb) and they were pointing down causing a mass of gas puddling in the intake port and causing back-fires and a lot of power lost. I took a more archaic approach and turned and bent the squirters straight and it took a lot of the lag out of the throttle, I wouldn't recommend this unless you are willing to buy new carbs if something goes awry.

Was any of the work done(I.E. head and cam:stock or aftermarket?) that will have a huge effect on how the bike runs. if that is the case it will take a skilled person familiar with a 750 to tune it correctly. even if that's not the case you will have a long process of tweaking doing it yourself. hopefully this raises a few questions or answers some. this also may be a unique situation.

[BlackMax]

Emery is WAY too rough for points you say??     Uum,  uh...well, I used 80 grit sandpaper to start, and then finished with 800 grit emery   I just wanted to make absolute sure that there were two clean contact points to send voltage to the coils.  I was out of patience I guess.     Well.......it fires so far     

 I'll keep an eye on it though.  The idle was set waaaaaaaaaaay too rich.   I'm wondering if the primaries are set the same way.  We'll see if the plugs foul out again in short order.

[mlinder]

Do your carbs have air screws? I... can't remember.
Too....
many......


carbs......

Anyway, if you have a fuel/air screw on your carbs lean it out. To like, 1 and 1/4 turn out.

I'm guessing yours don't, though, and really don't want to spend the time pouring over online documents trying to figure oout if they do.
So, if they do, lean em out.
Again, make sure your air filter is clean. I think we went over that already, though.

[TwoTired]

Emery is WAY too rough for points you say??     Uum,  uh...well, I used 80 grit sandpaper to start, and then finished with 800 grit emery   I just wanted to make absolute sure that there were two clean contact points to send voltage to the coils.  I was out of patience I guess.   

The grit in cheap "sand"paper is silica, which is a pretty good insulator.  Small particles break off and are left embedded int he soft point contact metal, and these bits don't wear nearly as fast as the point metal.  This leads to higher heating of the points and shortened life.
Don't be surprised if your points need reconditioning again real soon.

Only use metal or conductive abrasives on electrical contacts, like a points file.  You can burnish to a shine with unwaxed plain cardboard.  But, this latter step is only required for very low voltage point contacts with light spring closure pressures.

I recommend you obtain a spare set of points, and plan for early replacement.

[useless]

ok can someone help out here...I have the same issue, first thing i tried was sanding the points setting the gaps, messing with the timing, sanding & cleaning the connections to the coils...not getting anywhere. very frustrating. 2&3 run great...1&4 sputter and miss. '73 cb350f.  cheers.

[BlackMax]

If I had to go through this again, I'd:

1) check the plugs
2) check the wires for a good connection between the end and the wire itself
3) you said the points were fine.....just make sure you're seeing a nice spark
4) coil-  have the coil for you bad cylinders tested.  if bad, replace

If these things don't solve the issue, you've got problems with the carbs....and that's a whole other can of worms.

[HondaMan]

ok can someone help out here...I have the same issue, first thing i tried was sanding the points setting the gaps, messing with the timing, sanding & cleaning the connections to the coils...not getting anywhere. very frustrating. 2&3 run great...1&4 sputter and miss. '73 cb350f.  cheers.

Get a fine-pitch jeweler's file, flat, if you cannot find a real points file (they are kind of hard to find, anymore, but do work better). Gently but firmly file off all that sandpaper grit you embedded in those points last time. Burnish (I like to use white business cards from useless salemen) until they shine, then re-time.