Can't get above 1,000 rpm

Hey all,

Ran into a new issue today. Finally got the bike to start reasonably well, so I rode it to church. Then, coming back to it after a few hours, it would start, but I had to keep my hand on the throttle to keep it from dying. The crappy part is that I couldn't get the RPMs to go above 1,000. Zero throttle response, other than to keep it barely running. I sat there for more than 15 minutes, temp ran up to mid-line, no change. It wouldn't rev up and it wouldn't stay running. I even drove it around (very slowly) and nothing changed.

I went back tonight, and it fired right back up, with decent throttle response. So, I cut power, went and got my helmet out of the car, came back, and it wouldn't rev up again. Man, this sucks.

I've cleaned the carbs three times in the last few months. I can spray carb cleaner through the enrichment circuit and I can even see light at the bottom of the tunnel. Float height were spot on when last I installed the carbs (two weeks ago). A month ago I pulled them all apart and the pistons fall without any resistance. I guess they clunk. There don't appear to be any holes in the diaphragm. There is a blemish on one slide. Looks like it got lightly gouged, but it is smooth and the piston doesn't hang up at all. As I said, when I dropped the piston, it dropped straight down without any hesitation.

Fuel seems to be flowing. I had it on prime, and there was fuel in the in-line filter. I have the pilot screws turned out 2.75 turns.

All cylinders are firing.

Any thoughts? Suggestions?

 

Have you checked your fuel petcock, could be a fuel flow issue. Did you install a inline fuel filter? I had similar problems with my X , the pilot jets kept clogging. A fuel filter solved the problem.

 

Test the Inline Filter.
Some Inline Filters are Crap.

Remove it.
Look for the "Flow" pattern.
Blow through it.

2.75 Turns Out may not be enough.

The CLUE to your troubles is:

"Can't get the Bike to rev move than 1,000rpm's."

NOT Being Supplied Main Jet Fuel.

"Fuel (((seems))) to be flowing!!!
Why?
Because the Filter is full?
Bag the filter for a QUALITY Filter.

I'm betting 2-Bucks the Filter is Crap.

 

You may Think all cylinders are firing (when the problem is there) . Do you have a Colortune plug? Does the bike 'stumble' with throttle input. I'd say check your plug wires, caps, coils & then move onto the TCI. I know it sounds weird recommending to multiple people in the same week that their TCI is the culpret but it seems like the 25 yr mark is a kinda sorta 'experation date'! If you don't have a colortune purchasing one (in your case) could be used to help diagnose and fine tune your Idle mixture. I wouldn't have known my TCI was bad without one. Also, as a quick first check, when the problem is there, pull random plug wires one by one and listen for changes, if no change its probably not firing and you should experiance the same stumble

 

Sorry, I hope your problem is fuel flow, I've just been CONSUMED with the same Exact problem. At least you have a paper trail of posibilities. Good luck

 

also sounds like it could be the tank cap vent... where there's no air release and it doesdnt flow fast enough... when you park the bike and let it sit, the bowls will fill up and it will run off that and the fuel in the lines... then it's being starved for gas.

 

i had the same problem when i first got mine. only happened once in awhile. but if i disconnected the fuel line. then it would run.

it just sat at idle. never died. but wouldn't rev either.

one time it actually happened while i was out on the road.

i've cleaned out the petcock and carbs. haven't had the problem since.

 

Thanks for the suggestions. I'll replace the fuel filter. Just bought the thing with my last carb clean. Doesn't have 20 miles on it... But, they are cheap to replace. Not sure what a good one is like, though. I'll get one from the bike store instead of the car parts place. Should I look for one with a paper filter inside or the gold "stone" filter? I have the metal kind right now...

I did go through the plug caps. Cleaned the stock parts really well with a wire wheel and steel wool. Even wrapped the spring with steel wool, and twisted it down around the contact plate at the bottom. Saw shiny metal when I shined a light down there. After that, all caps tested to around 5 ohms (4.7 - 5.7). Also trimmed the plug wires. The bike starts great, now. And all headers are heating up.

I cleaned the petcock when I took the carbs apart the last time. I actually was wondering if I did something wrong when putting it back together. Not sure if I can goof it up that badly, though. I lined up the dimples and holes, so things should be good. And, I could see fuel flowing when I was testing my float height... I'll test the vacuum on it today. See if there is anything else I can check on it. I have a spare (thanks Mike!) if I need to use it, but the filter is kind of crusty...

How do I check the fuel cap, schooter? That seems plausible. Something to check, anyway.

 

Check the fuel cap by opening it up when it starts giving you a problem. If there is vapor lock, the gas cap is not venting air into the tank as the fuel level drops, so the fuel fights gravity adn doesn't flow. Opening the cap acts like a proper vent. If you hear a WHOOSH when you open the cap...that's also a sign.

Bigfitz52 just put a petcock rebuild thread up in the FAQ Suggestions. Check it out to see if you did anything wrong. Also, check the simple stuff. Did you mix the throttle and choke cables (it happens). Do the cables bind anywhere, and does the throttle cable actuate the throttle properly? Did you hook up the fuel and vacuum lines properly? Is your tank clean?

 

Thanks, manbot. I'll check fitz's petcock post.

The tank was kremed by a previous owner. Looks like crap, but the petcock prefilter is pristine. No gunk in the petcock, either, when I took it apart a few weeks ago. In fact, all I did was change out the o-rings and clean up the face plate. But, I might have botched the reassembly.

Now that I think about it... Last time I really was able to ride the bike, I was doing plug chops out on a local road. I remember that it died on me when I rode it home. A couple of times it acted like it was just loosing juice. I'd have to keep twisting the throttle just to keep it going. Then, when I had to stop at a sign, it just died. A few minutes later, it came back to life. Seemed like it was starved for fuel. So, I'm now thinking the cap might be the culprit.

In any case, I pulled out the little plastic, metal-type fuel filter and put in one of those big ol' clear view filters. Filled right up and the bike started up without any problems. Still having trouble with low rpm, but that is another issue I'm working on... Hopefully, the new filter will make a difference. Was a hassle to find an accessible space in the engine where it could sit, though! Its about twice the size of my previous filters. Hope it is worth the $10.

 

A small FRAM Mini-Universal Fuel Filter would have done the trick!

http://www.google.com/imgres?imgurl=htt ... s%3Disch:1

 

You know, Rick, I tried to find one of those. The auto parts place had something similar, but with a 2" diameter. Crud. Well, I'll keep my eyes open. For now the clear view is working ok.

Working over the fuel tank cap tonight!

 

Look in my petcock thread, toward the end I posted pics of all three styles of fuel filter chacal carries; I use the smaller straight-through type on my 550s and haven't had a problem.

 

Thanks fitz. I have had two of those style filters. Didn't have a problem. But, when I looked at the shiny see through filter, I though, "It's $10, it has to be good!" Yeah, I'm a sucker. LOL

The filter I just replaced was one of the straight through styles.

When I pulled apart my cap, I found that the rubber seal was worn through under the spring ring thing. Not sure, but I can't imagine that the cap works right if the rubber seal is compromised. I'll check my spare cap and see about swapping parts.

 

if the cap seal is ruined then your not vacuum locking. your releasing fuel vapors into the atmosphere instead.

we're all probably doing that by now. since these bikes are close to 30 years old.

 

Not vacuum locking, huh? Well, shoot. OK. So, there must be another reason why I can't get up over 1,000 rpm. I just tried again last night, and it did it again. Couldn't get it up above 1,000. Wasn't warm, either. So, I guess it isn't a heat-related issue.

This weekend I'll go back through my petcock per fitz's tutorial. I'll get it fixed up. Then, I'll do the piston bores in the carbs and reseat the diaphragms and see if that helps, too.

Would low compression be a factor? I just orded my compression tester, and should have it in a day or two, but I've had a sneaking suspicion for a while now that maybe I have low compression. Would that have an inconsistent affect on how well the petcock works, since it is vacuum operated?

 

Do a quick little Test.

Attach a Hose to the Fuel Bowl's Float Height Drain Nipple.
Put the Petcock on PRIME.
Unscrew the Fuel Bowl Drain Screw and collect the fuel draining from the Height Test Nipple.

See how well the Fuel is flowing to the Bowls.

 

I couldnt get my bike over 5k for a couple days.
Reseated the diaphrams, and PROPERLY saturated my UNI air filter and she runs like a champ again.

 

How are we making-out with this one?

This isn't something squirrelly like the Throttle Cable End having escapes from the Carburetor Mount?

What happens when you physically lift the Carb Linkage open???

 

im sure this isnt the problem but i will ask . have you changed fuel maybe you got a bunch of water in your last fill up. pull a spark plug wire put a good plug in it start it up check and see if the spark goes away over 1k try it on both sides worth a try

 

I've been too busy to mess with the bike for the last couple of days. I'll be back at it this afternoon...

The throttle cable and enrichment slide all seem to be working properly. The throttle linkage is moving smoothly, as it should. I'll try working it with my fingers to see if it makes a difference.

I'll pull the carbs a little later today so that I can go over the bores again and reseat the diaphragms.

You know, I haven't ever cleaned the K&N filter that is in it. It doesn't look dirty, and it seems to be oiled. But, maybe I'll clean it just in case.

I'll also check the spark above 1,000. I hadn't thought of doing that. Seems like a good thing to check.

 

So, I've done a few things to the bike to check stuff out. First thing I did was check fuel flow. Fuel flows into the bowls, which drain freely. Good flow out of the filter, too (I put the other, smaller inline filter back on).

I went back in and dressed the piston bores in the carbs. Touched up the needles, too. Checked all my jets and stuck a wire down the enrichment tube to ensure that it was clear, as well.

Took off the petcock and cleaned it up according to bigfitz's awesome sticky. Everything was cleaned, Dremeled, lapped, etc. The thing seems to be working great.

Still no joy. So, I finally got my compression tester and gave it a shot. I found 65, 100, 110, and 100 in cylinders 1, 2, 3, and 4 respectively. I put a little oil in, and wouldn't you know it, pressure went up to 90, 160+ in numbers 1 and 2 (I stopped after that because it got dark, but I could tell what the story is).

So, here's my theory... Is it possible that low compression isn't creating enough vacuum to pull fuel consistently? Sometimes it works, but sometimes I can't get it above 1,000 rpm. Even when it works, I can't get it to idle below 2,000. Would my low compression affect that?

What do y'all think?

 

As always...did you do the compression test with the throttle wide open?

But given those numbers...you can't expect to get your engine to run at all without compression. The MINIMUM compression in any cyclinder in the airheads is supposed to be 128 psi. Bad news - might want to start looking for a parts bike with an X motor - that has good compression! :x

Maybe someone with an X can give you advice on a rebuild...but one way or another that motor is shot.

 

Maybe check the inlets, (manifolds) to the head aren't really cracked and are well sealed also ? And valve clearances should be in spec before doing compression test.

 

Maybe check the inlets, (manifolds) to the head aren't really cracked and are well sealed also ? And valve clearances should be in spec before doing compression test.

 

Maybe check the inlets, (manifolds) to the head aren't really cracked and are well sealed also ? And valve clearances should be in spec before doing compression test.

 

Maybe check the inlets, (manifolds) to the head aren't really cracked and are well sealed also ? And valve clearances should be in spec before doing compression test.

 

Do it 4 times to be sure, to be surer, to be even surer and to be as sure as you possibly can. Sorry guys, this server keeps "expiring" the webpage, I didn't twig it was re sending this one each time.

 

Well, dang... I didn't have the throttle wide open. Would that make a big difference? I did have the engine warmed up, though...

I didn't check for leaks around my intake manifolds. The manifolds, themselves, are in pretty good shape. Could be that I have leaks, though. I'll get my propane torch out tonight and see if the engine runs any different when I blow some propane on the manifolds.

I do, thankfully, have a donor engine. I've been trying to rule out everything before swapping the engine. I have not wanted to give up on a good engine, but I'm thinking it might be time to move on. The thing is, I don't have any smoke at all. The compression change between dry and wet would indicate a ring issue, but without smoke?

Anyway, I didn't want to swap engines and find out that the problem wasn't the engine in the first place!