Carb rebuild, lots of carbon on top of valves?

[Jake]

Hello all. A fuel leak, proper gushing, after storage has prompted the carb rebuild I've long suspected was coming (partly because the secondary air filter element was found to have disintegrated when I got the bike). Thanks to Adam Frymoyer's guide, removal was strait forward. Upon looking down into each of the intakes on the engine I noticed allot of carbon deposits on top of at least one pair of valves. All had some, but one set had a little pile (3-4mm lump). I'm aware that the bike is probably miss firing and is under powered. I checked the resistance on the coils, and HT leads (with and without caps), the caps on the left bank are more than double the resistance they should be, as a pair, but without caps are in spec. Obviously I need to maintain/replace the spark plug caps on this side. My questions, to any one willing to advise, is:

The bike has been run for a few thousand km with a misfire and noticeable repeated fouling on the plugs of one bank. I'm over hauling the carbs....but do I need to be concerned about the amount of carbon that will be present in the cylinders?

Can excessive carbon damage the piston rings/valve seats?

Once the carb is sorted should I run a couple of tanks of fuel additive?

It's probably obvious to many of you that I've limited experience in deep maintenance like this. I enjoy it and prefer to do what I can myself, not least because I hate shelling out for often poor work by mechanics. I'll be going further than Adams guide because the fuel leak is down to a failed O ring on the fuel tube, necessitating a total strip down and rebuild...so wish me luck.

 

[oude geit]

Compression check will test mechanical components. Eliminate deep problems. All else is cleaning and spark.

 

[Kevcules]

Try to soak the carbon with something to loosen/soften it so it can be wiped away. Use a soft brush also. Try to get as much as you can.
For the misfire, hopefully the carb rebuild helps as well as check your wires and coil for proper operation.
I use MMO and Seafoam often in my fuel and the last time I had my air box off looking at my throttle body (fuel injected 1300) the valves were all shiny silver clean
Good luck.

 

[Al st1100]

check the vaccum fuel shut valve for fuel leaking into the vaccum hose. Pair valves are exhaust emmisions related and shouldn't cause misfires.

 

[Roger]

Dismantle the plug caps. The insides will unscrew - then you can clean up the internal spring and check the resistor. Hopefully your test will be better.....

 

[Jake]

check the vaccum fuel shut valve for fuel leaking into the vaccum hose. Pair valves are exhaust emmisions related and shouldn't cause misfires.

Thanks for response. Neither of these are an issue though as I deleted the fuel shut of valve and my UK spec 1999 bike does not have the Pair valve stock.

 

[SMSW]

1. The bike has been run for a few thousand km with a misfire and noticeable repeated fouling on the plugs of one bank. I'm over hauling the carbs....but do I need to be concerned about the amount of carbon that will be present in the cylinders?

2. Can excessive carbon damage the piston rings/valve seats?

3. Once the carb is sorted should I run a couple of tanks of fuel additive?

1. Probably not. A compression test or leak down test will tell you what you need to know.
2. Yes. But it doesn't happen all that often nowadays. They put cleaners in the gas and engine management is better than 50 years ago. The tests mentkoned above (in this post and earlier ones) will tell you what you need to know.
3. No fuel additive has been proven - in a well designed, independent study - to significantly affect our engines. There is lots of anecdotal evidence and belief systems run rampant across the internet but little to no factual knowledge here. Bottom line seems to be 'it cannot hurt' and this philosophy keeps a lot of businesses rolling in money. You might go to youtube and watch Fortnine's take on fuel additives. His point is some of them just might be capable of damage. If it makes you feel better, pour your favorite mix in the tank. If nothing else, it will improve your acceleration because your wallet is lighter and you are hauling around less weight on the bike.

 

[ST1100Y]

The bike has been run for a few thousand km...

Can you elaborate on this?
Use as daily, short distance, city commuter would explain some carbon deposits, as the engine never really warms up fully...
Stuck coolant thermostat will cause it to run too cold... again improper burning...
Also a stuck choke, maybe cable came off or linkage detached...
A too rich setting will impact like 45% of the lower RPM range... again cause for deposits and soothed plugs...

I'd perform a carb overhaul (new air filters, insulators, whatever you come across wile in there) and check the crimps on the voltage feed at the coils for possible loose contacts...
Then proper carb adjustments and syncing... should run like new after that...

 

[Jethro]

Replacing two plug caps? Why not the other two.Kinda like replacing one trailer bearing.

 

[afrymoyer]

Hello all. A fuel leak, proper gushing, after storage has prompted the carb rebuild I've long suspected was coming (partly because the secondary air filter element was found to have disintegrated when I got the bike). Thanks to Adam Frymoyer's guide, removal was strait forward. Upon looking down into each of the intakes on the engine I noticed allot of carbon deposits on top of at least one pair of valves. All had some, but one set had a little pile (3-4mm lump). I'm aware that the bike is probably miss firing and is under powered. I checked the resistance on the coils, and HT leads (with and without caps), the caps on the left bank are more than double the resistance they should be, as a pair, but without caps are in spec. Obviously I need to maintain/replace the spark plug caps on this side. My questions, to any one willing to advise, is:

The bike has been run for a few thousand km with a misfire and noticeable repeated fouling on the plugs of one bank. I'm over hauling the carbs....but do I need to be concerned about the amount of carbon that will be present in the cylinders?

Can excessive carbon damage the piston rings/valve seats?

Once the carb is sorted should I run a couple of tanks of fuel additive?

It's probably obvious to many of you that I've limited experience in deep maintenance like this. I enjoy it and prefer to do what I can myself, not least because I hate shelling out for often poor work by mechanics. I'll be going further than Adams guide because the fuel leak is down to a failed O ring on the fuel tube, necessitating a total strip down and rebuild...so wish me luck.

Hey Jake... First off, you don't have to totally break apart all of the carbs to replace the fuel tube o-rings. Remove the 4 screw bottom plate that holds the carbs together, then loosen up the two bottom carb pivot screws, so there's half the threads showing. This will give you enough room to wiggle out the fuel supply tubes without messing around with the linkages, etc. Use a big carpenters c-clamp to hold all the carbs together when re-assembling the bottom end. Leave all the bottom end screws somewhat loose until you've painstakingly assembled and snugged up the topside plenum. Then go back and tighten everything up.

I strongly suggest that you replace the spark plugs and ALL of the resistor plug caps. They are a maintenance item and are known to fail. The other two caps that tested good, aren't too far behind. At roughly $25 a piece, it's cheap insurance. While you're in there, have a good look at the the coils. The coil mounting bolts get rusty and leads to a questionable ground and a weak spark. It makes a huge "seat of the pants" difference in drivability when the ignition system is properly and cleanly grounded.

As for the chunks of carbon on the valves, you can rotate the engine over and get that cylinder on TDC of the compression stroke. Fill the intake runner with carb cleaner and let it soak for several hours. A smaller brass pipe cleaner will knock off most of the carbon. Put a thin rag on the end of the pipe cleaner and clean out the valve stem and intake runner. When the bike is up and running, add a heavy dose of Chevron Techron fuel system cleaner. This will clean up the valves rather nicely, within a tank full. Or, you could just add the Techron and get them cleaned up within several tanks.

Good Luck!

 

[Jake]

Can you elaborate on this?
Use as daily, short distance, city commuter would explain some carbon deposits, as the engine never really warms up fully...
Stuck coolant thermostat will cause it to run too cold... again improper burning...
Also a stuck choke, maybe cable came off or linkage detached...
A too rich setting will impact like 45% of the lower RPM range... again cause for deposits and soothed plugs...

I'd perform a carb overhaul (new air filters, insulators, whatever you come across wile in there) and check the crimps on the voltage feed at the coils for possible loose contacts...
Then proper carb adjustments and syncing... should run like new after that...

Mixture of use (short journeys a couple of times a week, long (2.5hr) run search way once or twice a month...then it stood for 8+months). I'm into the carb and about to start another tread for advice. Different and smelly kettle of fish.

 

[Jake]

Hey Jake... First off, you don't have to totally break apart all of the carbs to replace the fuel tube o-rings. Remove the 4 screw bottom plate that holds the carbs together, then loosen up the two bottom carb pivot screws, so there's half the threads showing. This will give you enough room to wiggle out the fuel supply tubes without messing around with the linkages, etc. Use a big carpenters c-clamp to hold all the carbs together when re-assembling the bottom end. Leave all the bottom end screws somewhat loose until you've painstakingly assembled and snugged up the topside plenum. Then go back and tighten everything up.

I strongly suggest that you replace the spark plugs and ALL of the resistor plug caps. They are a maintenance item and are known to fail. The other two caps that tested good, aren't too far behind. At roughly $25 a piece, it's cheap insurance. While you're in there, have a good look at the the coils. The coil mounting bolts get rusty and leads to a questionable ground and a weak spark. It makes a huge "seat of the pants" difference in drivability when the ignition system is properly and cleanly grounded.

As for the chunks of carbon on the valves, you can rotate the engine over and get that cylinder on TDC of the compression stroke. Fill the intake runner with carb cleaner and let it soak for several hours. A smaller brass pipe cleaner will knock off most of the carbon. Put a thin rag on the end of the pipe cleaner and clean out the valve stem and intake runner. When the bike is up and running, add a heavy dose of Chevron Techron fuel system cleaner. This will clean up the valves rather nicely, within a tank full. Or, you could just add the Techron and get them cleaned up within several tanks.

Good Luck!

Thanks for the advice. I went ahead and got stuck into the carbs. Glad I did, because there are a number of issues. I'll be posting a new thread for advice on those. Appreciate your response.