Cold Exaust Header - Valves or Carbs???

[janksolid]

My 750ES is running rough. Idles OK but really fluffy mid range. One exhaust header is cold. Good spark.

Where do you think I should go first? Valve clearances or carbs?

I know, I know I should do both...

[hampshirehog]

Chicken and egg - however there's no point in sorting your carbs if your valves are out.

Are you running with standard pipes and air filter? That could also be the problem.

[janksolid]

Yeah. Think I'll sniff round the carbs first though. Bike was running OK. Just got worse over a few weeks.

Non standard pipes and filters plus a couple of other non standard parts ;-)

[atb1998]

carbs first..

[woodman]

Clean the pilot jets, one is plugged. Get some guitar wire to clean it or a new pilot jet

[BassCliff]

Hi,

I concur. Adjust the valves while your carbs are disassembled and soaking in carb dip.

That's a nice looking motorcycle. Thanks for the picture.


Thank you for your indulgence,

BassCliff

[hampshirehog]

Nice looking GSX with some tasty mods you've got there - keep it locked up or I'll sneak round and pinch it.

If the problem has gradually deterioated over a period of weeks and it was running fine before that would leave me to suspect the valve clearances are closing up - assuming a reasonable amount of running time and no change to the carbs.

Carbs don't usually gradually deterioate over a few weeks - they tend to change suddenly as something gets blocked. They will gently drift out of synch over time and will very gradually varnish up but it's usually over a longer time period. Having said that, they may have been shifting set up on their own for a while and the last few weeks has seen them 'tip over the edge' so to speak.

'Fluffy in the mid-range' is often a carb fettling issue, especially with CVs, when swapping to pods / exhaust, though I guess that if it was running fine before then someone has sorted this out already.

If you haven't checked the valves for a while you should really make sure they're ok - you appear as if you know that! Letting the gaps close up too much can leave you with a headache to sort out later.

Cliff - we aint as lucky as you Yanks with the carb dip. My guess is it's banned over here as it might be considered more risky to health than cotton wool or more damaging to the environment than air. We have to do it the hard way - by hand and using whatever detergents we can sneak out of the kitchen

[bmac]

cold header

I just ran into the same situation last weekend on my 82 850g. Had popping out of carb and exhaust at times at the of end riding season last year. So, before I rode it this year decided to pull the carbs and check all the internals, cleaned the pilot jets for hard starting and reassembled. Went to sync the carbs and wanted to adjust the mixture screws first for the best mixture when noticed #4 wouldn't make any difference on adjustment. Pulled plug and grounded it to the head and had spark. Plugs were nearly new. Anyways replaced the plug and the cylinder fired. So, moral is to check everything and take nothing for granted. bmac

[Nessism]

I'd also focus on the carbs but your question makes me wonder how long it's been since you've adjusted the valves? You check them are the regular interval don't you?

[BassCliff]

Cliff - we aint as lucky as you Yanks with the carb dip. My guess is it's banned over here as it might be considered more risky to health than cotton wool or more damaging to the environment than air. We have to do it the hard way - by hand and using whatever detergents we can sneak out of the kitchen

Hi Mr. hampshirehog,

Indeed, use whatever it takes. Lemon juice, tomato juice, molasses, whatever you've got on hand. That's why I used such a generic term, "carb dip", rather than "Berryman's Chem-Dip for Carburetors". We can't even get "the good stuff" any more due to EPA restrictions. They've watered it down.


Thank you for your indulgence,

BassCliff

[Don-lo]

Anyways replaced the plug and the cylinder fired. So, moral is to check everything and take nothing for granted. bmac

Good moral. Fouled plugs happen easily and are sometimes difficult to see. Fortunately, easy to check (swap a known good one with a questionable one). But It really isn't efficient to check or rebuild everything randomly. Check the easy things first, then use procedures to eliminate or pinpoint systems. Swapping known good parts with questionable is a big procedure. Bypassing is another biggie: running 12+ volts directly to the coils connection tells you if voltage loss is a problem, and a shot of starting fluid can tell you if fuel is getting to the carbs. Shop manuals have some good troubleshooting tips in them.

Anyways, the original question was where to check first:valves or carbs. A compression check should give you a good idea: low compression > valves, good compression > carbs.

[janksolid]

I'd also focus on the carbs but your question makes me wonder how long it's been since you've adjusted the valves? You check them are the regular interval don't you?

Only had the bike a few weeks and so not looked at the valves yet.

It feels kinda "carby". Could just need balancing maybe...

Probably a blocked jet though. I can actually SEE the carbs being pumped around on their rubbers. Never seen that before!

I've only just finished refurbing the carbs on my other 750 and don't relish the prospect of pulling another set. Sun is shining. Just want to get riding...

[twinapache]

Yep. Time to yank the carbs, and give em a good cleaning. Don't forget to clean the idle fuel screw orifice real good, and the pilot jet. Bench syning them while they're off will get you close, till you find a friend with a carb synchronizer.

My money's on the carbs, but you may as well adjust the valves too while your at it, for good preventative maintenance.

Check out Basscliff's website. Tons of good info there to help you out.

[AOD]

There's no need to dip carbs that are running relativly well. I've never dipped carbs, I use a good carb cleaner, brushes, etc, and a small bowl to soak the jets in when dissasembled.

Regarding this specific issue you need fuel, air, and spark at the right time to make heat. If you're getting spark, is the plug wet?

~Adam

[janksolid]

OK. Pulled the carbs yesterday and gave them a good clean. They were a quite gummy. I think the bike had been laid up for a while before I bought it.

Popped the carbs back on, put the fuel tap on prime and spun the engine over a few times. Flat battery. Charged it overnight.

Now I've got a completely dry carb on the cylinder that wasn't firing properly before. No fuel in the float bowl.

Needle valve???