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Possible Valve problem?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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I'm having some trouble with my '79 425EN. I can't seem to get it to rev above 4500RPM. The bike sat untouched in a barn for 17 years before I got it. I was having some rich running problems so I talked with a friend and he told me to remove the airbox and watch the venturi slides in the carbs. I did this and found them both to be working. But I took the carbs apart thourougly cleaned them and put them back together again and balanced them. Same thing everything works. The odd thing that I noticed is that both times I watched the slides I noticed that the carbs blew Air/Fuel mix back out the airbox side of the carbs. Right side was slightly worse than the left but both had the same problem. I have yet to tear the top off the engine and check the valve shims or do a compression test. Has anyone ever seen this problem before, or have any ideas what could be done to try and solve this.

I have never done a valve shiming job or valve replacement on anything before, I've read the procedure in my repair manual but still am a little afraid of it. Could it also be that the cam timming is misalined on the intake cam. I have no history of the bike and much of the bike was missing when I received it.
 
Check the valve clearances first, it's not that hard to do. Then do a compression test
 
checked compression

checked compression

Sorry for taking so long, It was a crazy week. I picked up a compression tester yesterday and just tested the compression on both cylinders. 140 PSI on both cylinders. I haven't gotten to look at the valve shims yet. It is on my to do list.

I'm guessing that this 140 PSI means my valve are good becuase it is within the specs called out in the manual.

Here is how I did the compression test (cold engine).
1. Remove both spark plugs
2. insert hose from compression tester into cylinder.
3. hold throttle wide open
4. rotate engine until needle on guage discontinued upward movement (about 4-6 compression rotations)
5. Repeated on other cylinder

With readings of that good of comprssion I am trying to figure out what could be causing the fuel to be blow out the intake side of the carb. Is it possible I have a sticky valve? What are the other possibilities?
 
Planned For tonight

Planned For tonight

After scoping around today I found out about doing a leakdown test. Turns out I have all the stuff to build the tester at home in my toolbox :lol: . I will slap one together tonight and give it a test. I know that the intake valves have quite a bit of carbon on them and I may be able to just clean them if they are indeed the problem. Hopefully I don't find anything to bad or costly. Otherwise the rebuild is shelved until next summer. (Why do cars have to cost so much to fix? :x )
 
Go ahead and check the ignition timing. If it has points go ahead and replace them along with the condensers, should'nt cost to much.

Also check fuel flow from your petcock to the carbs, and you may want to drop the bowls one more time just to make sure the jets and float needles are still clean. 17 years in a barn make's me think it's a fuel problem.
 
RacingJake said:
Go ahead and check the ignition timing. If it has points go ahead and replace them along with the condensers, should'nt cost to much.

Also check fuel flow from your petcock to the carbs, and you may want to drop the bowls one more time just to make sure the jets and float needles are still clean. 17 years in a barn make's me think it's a fuel problem.
Click to expand...

this is not a suggestion but just a comment

Say jake, i was thinking that the air blowing backthrough the carbs while just cranking the engine may be a normal thing. after all the cam timing is usually quite sloppy on startup even with a stock cam. Yes/No???
 
Might be Scotty

I'm thinking if it's to riched then the fuel may be blown backout, or if it's an ignition problem and the engine won't rev above a certain amount and the throttle is wide open it might be the cause too.

???
 
Thanks for the info guys. So here is what I found last night. My leakdown test shows me that both cylinders seem to be holding preasure just fine. That is a huge relief.

As for the breaker boints I just replaced them about 3 weeks ago. I had a hell of a time getting it to time correctly though. It seemed as if the new points didn't fit the advance cam right [can the cam go bad?] and had to fiddle with the breakers and the timming plates until I got the darn thing to time correctly. I may check it again though becuase once again I am back down toward 3500 RPM and it begins to miss and stall after about a mile of ridding full throtle (40 Mph in 6th). But the plugs are as black as they could be, which still leads me to belive that there is something else still wrong.

Last Time I dropped the bowls I used a peice of wire (about 40 gauge or so) to run through the jets and the passages that I could find. I am getting close to starting to lower the main jet on each carb about a 1/4 to 1/2 turn and see what that does. Hopefully that will lean the mixture slightly.

Odds are that it is a combination of things.
1. Mixture from carbs is way to rich
2. Timming is off or coils are bad
3. Something with the top end (Valve shims, Cams not put in properly)

My GF has plans on Thursday with one of her friends so that leaves me the whole night to tear off the cam cover and look at things for the first time. (Watch it be that things are off by a tooth)

Hopefully it is just a combination of simple things.
 
Are you trying to ride it without the airbox and airfilter installed? If it's anything like my 1100, it won't rev without it.
 
No I do have the air box installed, and Although it is not the factory filter I do have one installed in the cage.
 
Last Time I dropped the bowls I used a peice of wire (about 40 gauge or so) to run through the jets and the passages that I could find. I am getting close to starting to lower the main jet on each carb about a 1/4 to 1/2 turn and see what that does. Hopefully that will lean the mixture slightly.
Click to expand...
If you didn't do it already, take the carbs completely off and disassemble. The best way to clean them is to use a chemical dip, but the spay stuff works pretty good also. It sounds like you have an air compressor - so blow the passages out. I'm not sure how good you cleaned them using the method you described.
 
I've had them off three times now for a good cleaning. First two times used the spray carbcleaner and the air compressor. Last time I used an electrical component cleaner on them. It worked really good becuase it pull all the varnish right off everything. Like I said the only thing that I can think of with the carbs now is that the jet height is wrong. I may be wrong but I thought the jets on the GS425 were supposed to be screwed in all the way. I may be worng and that is something I am going to be experimenting with.

I spoke with my friend again yesterday who is a suzuki racer. I cannot mention his name he has enimies here. He figures that I have a cam out of timming with what I have been finding. Tommorow will reveil the truth.
 
The jets should be screwed all the way in - and tight.

You could have a cam that skipped a tooth.
 
andycasper said:
I spoke with my friend again yesterday who is a suzuki racer. I cannot mention his name he has enimies here.
Click to expand...

Sence your friend rides a Suzuki he can't be all that bad, now if he rides a Honda then that's a different story. 8O If he rides a HD then so much the better.:twisted:
 
RacingJake said:
Sence your friend rides a Suzuki he can't be all that bad, now if he rides a Honda then that's a different story. 8O If he rides a HD then so much the better.:twisted:
Click to expand...

Well he will only ride his suzuki, He bought his wife a HD and he calls is his girly bike.
 
Swanny said:
The jets should be screwed all the way in - and tight.

You could have a cam that skipped a tooth.
Click to expand...

Cool that is good to know. I couldn't find anything about adjusting the jets in my namual and that is why I questioned doing it.

The bike was beat bad before I got it and I figured it is most likely a cam is out at this point. Hell the bike had studed dirt tires on it when I got it. I'm suprised the bike is in as good of condition as it is.
 
The worst of luck

The worst of luck

Well everyone. Here is my story from last night. SO... I get home from work and tear the top off the engine. No big supprise. The last goon to work on the engine had set the cams up for the GS450 (18 pins) instead of a GS425 (20 Pins). So I tear out both cams, adjust everyting put it all back together. Guess what. The engine sounds tons better. But still less power than it had. So I figure OK something else must be off. Check the timing. Hmm. still good. Balance the Carbs. Those were way out but I figured they would be. Ok Whats left. Valve shims. Not getting done due to lack of revenue at this point in time. No oil change either, Might try that tonight. I think I might have to much oil in the engine. Can't tell becuase the stupid window is fogged on the bike.

So I decide Hell I'll take it for a ride and see if it gets better. Let the engine idle for a bit while I put on some riding gear. Get on and take off. Well engine wont get above 3 grand under load. And after about 5 minutes of riding I couldn't get above 2 grand. Yeah that was unsettleing. Being exhausted due to the fact it was 10 PM I put my bike away and turned my attention to my car that also needed repair again last night [stupid money pit].

At this point I'm out of Ideas. I figure that most people are going to say timing or coils. Well I checked the timing, and I have no idea about the coils. If that is what It is then it gets added to the project for next summer. $50 left in the budget and school only 1.5 months away. Time to get busy saving.

:?: If anyone else has any other ideas let me know please. :?:
 
Oil makes no difference

Oil makes no difference

I did the oil change yesterday. No difference noticed in the preformance of the engine. Still under 3 grand. I'm going to bring home an oscilliscope and a current probe tonight and check the coils. At this point I'm not sure where else to check. Although I probably should look at my plugs now and see if they are the color that they should be.

No matter what I find it will be storage time for the old bike. At least if I find it is the coils I can continue my repaint job this winter. Otherwise why waste my time on a bike that doesn't run.
 
Found the culprit. It is the condesers that are mounted with the coils. So those are on order and all will be good.
 
Wow, I'm impressed. What a nightmare huh?
Keep us posted when you get the condesers.
 
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