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Do you think it is a valve issue or a carb related issue

  • Dirty carbs

    Votes: 4 80.0%
  • Burned valve / head issue

    Votes: 1 20.0%
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Mexican Hard Shell Taco
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Discussion Starter · #1 · (Edited)
UPDATE:

Update: Cleaned the carbs, bike still runs like crap!

Damn, what a waste of time. However I found that the airfilter wasn't properly installed, and that I'll have to get new individual air filters...

Will try to get a new sparkplug boot tomorrow.

Any other ideas???

END OF UPDATE



Well, as many of you know I bought this Can-o-tuna 750. The bike had been sitting for quite a bit of time, so I performed several preventive manteinance tasks. Adjusted the valves, changed a fork seal and adjusted the head bearings (that needs to be done again, still lose).


The bike used to hesitate from the line, but ran good at high RPMs. So I added carb cleaner to the gas, and that helped a lot.

However, today, after riding it I came to a speedbump and after that the bike ran like $hit! It seems to be running on 3 cylinders until aproximately 5K rpms. If I give it a little bit of throttle it will hesitate a lot, give it more gas and it seems to pick up faster and sometimes by 3000 rpms it is running fine.
Also the hesitation is worse according to the load, for example, when comming from a full stop, have to rev it up a lot for it to get going!

What can it be? I'm scared of the posibility of having a burned valve because of the adjustment, but I also think that maybe the carbs are gummed up and that the carb cleaner just losened the crap and now one carb is not working.

From what I can tell, the bike never had a valve adjustment before, but some valves were well within specs, and I adjusted the rest to be more or less like the ones I didn't touched (within spec).


I don't want to take apart the carbs, too many small pieces and I've never worked on something like that, so if the general agreement is that it is carb related, I'll take it to a shop to have them cleaned, adjusted and sync'ed. If it is a bad head, I'll just dump the bike as a hot potato!
 

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Autobots! Roll Out!
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If you think you did the valve adjustment right, I'd move right to the carb. You're comfortable working on the valve train but not a carb? C'mon brotha, take that stuff apart!
 

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Truck said:
If you think you did the valve adjustment right, I'd move right to the carb. You're comfortable working on the valve train but not a carb? C'mon brotha, take that stuff apart!
+1 Just take your time and do them one at a time. Not as hard as you think. I'd also check your coil connections to your plugs since you said it happened after you hit a speedbump.
 

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Mexican Hard Shell Taco
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5,896 Posts
Discussion Starter · #5 ·
Well, I'll check the carbs. I'm comfortable tearing engines apart, but I hate working on carbs!!!

I find them to be extremely hard to adjust properly. Engines, if everything is torqued fine, and adjusted fine (and that only takes sight and a feeler gauge or a micrometer) you know it will work. But carbs, you just assemble them and hope they do their black magic properly, and if they don't, you are in deep isht...

But I still would like more opinions, what would be the symptoms of a burned valve?

Here is a picture I took from the valvetrain and how much I dismantled the bike. By the way, I already found something I hate about sportbikes, and it is the fact that even the most simple task requires a lot of disassembly!

Edit: looks like the jpg compressor does not like red at all, I even tried to use a lower compression this time (30%)
 

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Mexican Hard Shell Taco
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Discussion Starter · #6 ·
Oni said:
+1 Just take your time and do them one at a time. Not as hard as you think. I'd also check your coil connections to your plugs since you said it happened after you hit a speedbump.

I also thought of the plugs, as one sparkplug boot is broken, but it is making good contact.

Think I'll have to dig into the carbs...


ME = :urowned
 

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Mexican Hard Shell Taco
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Discussion Starter · #7 ·
By the way, when I rode it today I was already scraping the pegs!!! My God, what a wonderfull feeling!
 

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Süsser Tod said:
I also thought of the plugs, as one sparkplug boot is broken, but it is making good contact.

Think I'll have to dig into the carbs...


ME = :urowned


This, to me, tells what to work on first. Since you are scared of working on the carbs, work on the simple stuff first.
KISS = keep it simple stupid

If the sparkplug boot is broken, it might not be making the proper contact to fire the sparkplug.

Replace the sparkplug wires first, then go from there. It probably needs new ones anyways.

Another thing, if your bike has a fuel filter, have you replaced that? Have you cleaned out the tank? Look in it to see if it is rusty. If so, you need to re-seal the tank.
 

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Mexican Hard Shell Taco
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Discussion Starter · #10 ·
Tank is not rusny nor seems to be dirty. The plug is working fine, that I know for a fact, as it only happens at low rpms with high load. If I disconnect the sparkplug the bike won't even startup. So it must be working.
 

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Just happen to me yesterday. It hit a bump and my coil came off the spark plug. Found it out by the clicking of the spark.
 

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Mexican Hard Shell Taco
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Discussion Starter · #12 ·
Update: Cleaned the carbs, bike still runs like crap!

Damn, what a waste of time. However I found that the airfilter wasn't properly installed, and that I'll have to get new individual air filters...

Will try to get a new sparkplug boot tomorrow.

Any other ideas???
 

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im thinking its the sparkplug wire too. keep us updated.
 

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Sport Tourer
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Sparkplug boot broken = Spark jumping to cylinder head. Try replacing that. Also, check for fowled plugs.
 

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Hardass!
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Süsser Tod said:
Tank is not rusny nor seems to be dirty. The plug is working fine, that I know for a fact, as it only happens at low rpms with high load. If I disconnect the sparkplug the bike won't even startup. So it must be working.
Arrgh dude! Go easy, then hard. In reality, it is very hard to burn a valve on a bike unless you ride it headerless.
I had a similar problem to where I could actually hold my hand to the pipe while running and had good spark.
It turned out to be a dirty jets. Add the miss, the bump and you have bad contact, not a headjob in order.
By the way, the tank doesn't have to be rusty, its what you INTAKE into the carbs thats the problem (air and fuel), being your air filter was on wrong is a good indicator of poopoo in the carbs. :bitchslap
Cleaning the carbs with a can of carb cleaner is not going to do it. Take the jets out, look at the small holes (small as a needle) and soak them in carb cleaner (berrymans) run some needles through the holes, and re-soak them.
Also make sure your air/fuel adjustments are equal. Replace ALL wires, not one, cause its a smart idea.
 

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Mexican Hard Shell Taco
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Discussion Starter · #16 ·
That is what I did, used two cans of spray carb cleaner. Dissasembled the carbs, cleaned every individual duct, one by one. And that is some strong i$sht!!! My skin was burning from the contact with the carb cleaner and I couldn't keep my eyes open!

Tomorrow I'll buy the new sparkplug boot and some individual air filters (one per carb).

The carbs were dirty, but thats it, bike runs the same with the carbs clean.
 

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are you using compressed air in the carbs, mine wouldn't get clean w/ just carb cleaner i had to spray the crap out with compressed air
 
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