Top end rebuild (Stuttering, Elec. Issues Prior) (Pic heavy)

I'm trying to track down an issue that started once I got home from the ride to Pennsylvania. Under hard acceleration, the engine bogs/stutters a little bit. It's especially noticeable around 4th gear, 45mph, 5k RPM -- I give it a good bit of gas, and it hesitates, and after two or so seconds it starts to pull.

Normally this would be a simple fix, but I've tried all the obvious things I could think of and nothing affects it.

In the past two weeks I:

- Got a new air filter

- Changed the oil

- Changed the plugs

- Put the valves in spec

- Cleaned the carbs

- Set the floats

- Adjusted the carbs with a Colortune

- Synced the carbs

- Rebuilt the clutch

- Checked all vaccuum hoses/boots

- Checked the resistances on the ignition coils

But no luck, still hesitates under hard acceleration. Sometimes it even feels like it's going to cut out. What haven't I checked?

It can't be anything like wrong jet size or something like that, because it always ran GREAT. After the 1,300 mile trip, something changed or broke or moved or wore out.

The only thing I have yet to check is the electrical system behind the ignition coils.

 

Re: I need your brains

Check the slide diaphrams for leaks. Take them out and hold up to a light. You should not see any light comming through, pay close attention to the outside and inside edges. Pull the diaphram a little and look for cracks. Check the slides and make sure they moove frely and pass the clunk test. Check your plugs, they are probably a little black from soot.

 

Re: I need your brains

You forgot the FUEL PUMP. Your bike has a fuel pump. Maybe you have a loose wire; or a piece of crud got into it.

Sure sounds like fuel delivery, unless you have one or more spark plug caps that are loose (or their CORES are coming loose.) Look inside the plug cap, there are two screwdriver slots on either side of where the top of the plug goes; ensure the resistor core isn't loosening up. You might also want to unscrew the caps from the wires, "lop off" about 3/8" and screw the caps back on.

But I vote fuel delivery.

 

Re: I need your brains

mlew, I did thoroughly check the diaphragms. No cracks/tears or anything of the sort. Also polished the bores real well so they clunk very satisfyingly.

Fitz, I checked the coils and wires last week, even lopped a little bit of the end and screwed them back in like you suggested. Everything about the coils checked out. Could it be anything electric before the coils?

I have not tried testing the fuel pump -- next thing I'll do tonight. It was odd to me because when I checked the float levels last week they were really low (well, not really low, but just out of spec) and I thought "well daggum that has to be it"...but now that they are set correctly there is no change. You could be right that the problem is getting fuel to the carbs. I am running a fuel filter -- no gunk in there -- and the petcoque is new.

 

Re: I need your brains

Is your exhaust and intake stock or have they been modified in any way? I'm curious to know what color the plugs are.
Fuel delivery is a good possibility, make sure your bowls are staying full first. The location of that filter is also critical, don't mount it to high or the pump will have a hard time pushing fuel to the carbs.

 

Re: I need your brains

Everything is stock.

I just checked the plugs. They come out very light brown -- almost too light. At least that should tell us that it's a lack of fuel rather than too much.

The fuel filter is half way in between the pump and the carbs (that hose is probably about 6-7 inches long). The vacuum line from the intake to the fuel pump could be in suspect. Need to check that too.

It runs really well, better than it ever has, except for that first little but o' throttle.

 

Re: I need your brains

The wire lopping and screwing back on was in reference to the spark plug caps. Also be sure the resistor cores inside the plug CAPS aren't working loose.

But I agree it sounds like fuel delivery.

 

Re: I need your brains

Update on this:

I re-tubed the whole fuel system, from the petcoque to the carbs, put on a clear fuel filter, cleaned/tested/rebuilt the fuel pump, replaced the vacuum hose from the #2 intake to the fuel pump....same result.

A plug chop would tell me everything I needed to know -- so I chopped the plugs and they were white. Looks like my gasoline is playing hide and seek.

!!

Floats are correct, even a little on the high side. Like mlew said, it could be the diaphragms, which I already throughly inspected. Time to inspect them again.

 

Re: I need your brains

Plugged gas cap vent?

 

Re: I need your brains

Update on this debacle:

I "rebuilt" the gas cap. It was in good condition, nothing out of the ordinary like dirt or old gas clogging it up. Same bike performance.

Then I re-cleaned the carbs, doubled checked the diaphragms, but everything is good as new. Bike still hesitates.

So then I realized the last major thing I did was service the valves, so I checked the valve clearances again. They are still in spec.

Finally, last night I realized I hadn't run a compression test in a while. All plugs were pulled, and I hooked up the gauge to #1. Wide open throttle aannnndddd....the starter turns over a couple times and the battery starts to die. Which is odd, because I have been riding every day trying to diagnose and the battery should have been fully charged.

I let the battery charge overnight, and this morning I run the test.

#1 165
#2 156
#3 155
#4 162

The manual recommends 145-167. WHEW Ok, no leaky cylinders, but now I'm starting to think I have a problem with my battery or charging system. ON TOP OF hesitation in acceleration.

This is the point I start to feel like a dope, after all the advice I've given other people but I can't figure out my own simple problem! :roll:

 

Re: I need your brains

Unscrew the plug caps and "OHM" them out, just the caps.

Replace the plugs with brand new ones.

However: Your "battery and/or charging system problem" could be related...

(Nice compression numbers, BTW.)

 

Re: I need your brains

The caps check out. Checked them all when I snipped a bit of the coil wire a couple days ago. They're only a year and a half old (I replaced them all when I got the bike). I just got done disassembling them all and inspecting the insides.

New plugs, check.

And you're right -- the battery is on the charger now, and if I go take a ride when I know the battery is fully charged and there's no stutter for a short distance, it could very well be electrical.

Gonna break out the multimeter and see what voltages the battery is giving me.

I'm surprised about the compression numbers. This bike was one of those "needs to be rescued from the hands of the abusers" cases.

 

Re: I need your brains

I really don't see ignition problems causing white plugs on a plug chop. Since the symptoms match fuel starvation, I think you were on the right track originally.

Kind of a hard thing to check off of a dyno, though. Is the fuel filter clear (as in see-through)? If so, can you compare the fuel level versus any air bubble in the filter when the bike is running well to when it's started bogging under load?

Is the filter new? Old? Did you try a new one?

Does you setup allow you to run on Prime? If so, try that to see if it changes or removes the bogging issue.

 

Re: I need your brains

Yea, no matter what I've been working on, it's ringing in the back of my head "The plugs were white...no fuel."

The fuel filter is brand new, and clear. I positioned it so I can see it while I ride. It stays full no matter the riding conditions.

I checked the petcoque, too. Same problem even when set to prime.

It is good I checked the electrical system, though. I do indeed have problems in that department. The battery is reading 12.8v @ 5k RPM, which is well below the recommended 14.3v - 15.3v. Looks like the lean problem is going to have to go on hold while I slap in some new alternator brushes.

The more I ride it, I realize the stuttering before acceleration only happens sometimes, and even then only below 5k RPM. Sometimes I'll be a cruiserist at 4.5k RPM and punch it, and it will stutter for two seconds and then accelerate, sometimes I'll punch it and it-will-fly.

And I'm pretty confident it's not the carbs -- you can only clean and rebuild those so many times before you go to bed at night and have dreams about them, which is the point where I'm at with 'em.

(thinking out loud) It's something that's keeping gas from all four cylinders. If a float was set wrong, they'd all have to be set wrong. If a boot was leaking air, they'd all have to be leaking air.

 

Re: I need your brains

Try getting it warmed up and see if you can reproduce the problem.....once you can reproduce it consistently, then turn the choke on a little bit and crank the throttle again.......this adds fuel from a separate circuit from the normal pilot and fuel circuits..........if, with the choke on slightly, then you've confirmed it's a fuel delivery problem, and that narrows your search a bit.

 

Re: I need your brains

Just got back from watching the NHL game @ Taco Mac -- darn those Red Wings.

However, the stuttering got progressively worse as the engine warmed up. Once it got to optimum running temp (about 10 mins of riding, smooth 1200 RPM idle w/ zilch choke), any acceleration I did made the engine sputter and almost cut out -- you'd think it was running rich! Basically had to take the roads where I could coast home.

Chacal, while it was sputtering @ 1/4 throttle, I gave it a little choke (then a little more and a little more) and there was no change. No positive change, at least. It started to bog AND sputter. Bog like it's running rich. Sputter like it's....lean?

When your bike is warmed up properly and you give it choke -- you know what I mean -- it bogs because you dumped a bunch of gas in there. That's what the bike did as I was riding and pulled the choke... except it still sputtered and hesitated as well. This is where my brain explodes.

I need to stop riding it. Probably doing more harm than I realize.

 

Re: I need your brains

I don't suppose it could be something as simple as a bad tank of gas

 

Re: I need your brains

I wish! I suspected that at a point, and now I have like 11 quart-sized oil containers in my garage filled with gas, haha.

 

Re: I need your brains

You mentioned you re-tubed the fuel lines. I had a problem much like yours and it ended up being the new fuel lines I'd installed. What was available was a blue plastic aftermarket variety sold by a local bike repair shop.

What was happening was the bike after some running became hot around the rear of the carbs, that was all the fuel line needed to bend over on itself & it started choking the supply. Repositioning the line would get it running again but it was a temporary fix & invariably it would shift and bend badly, I had to replace it with line that was more rigid & less prone to a case of the bendys.

Just relating my prior joy...

 

Re: I need your brains

Try running her with out the fuel filter. I hand a lack of fuel problem on my 750 and it turned out that the filter was causing fuel starvation.