Carb Spitback Help??? its getting to me now.

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Monty
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Sun May 04, 2014 5:44 pm

https://www.youtube.com/watch?v=rgsl3Ny ... 0KOSmKJYqA
I hope the vid turns out OK.
Muggy 185 Jetex normally through the air box. JL Snail
I was a bit previous with my statement about spitback on my wandering timing thread.
I have gone back to basics and am now running static timing at 17DBTDC. it was wandering all over the place but after a new BGM stator and CDR its stable. I did try an M Tech again but it was running like a dog so it came off again.
So after 3 weeks of buggering around Im back to square one. So much spitback it wont run with the carb rubber on. The rubber now has 2 holes that let the spitback escape but its straight down onto the pipe. It starts and runs but not with the rubber on. The vid is a reamed out 26mm that is not set up but its spitting the same as the 22mm I have run since I built the engine.
The problems all started when I lost some top end. I stripped it to find stuck rings round the ring pegs. The plating had come off in several places so it was sent for replating with a new piston. Got it back, rebuilt and holed the piston with what may have been a loose carb manifold.
At that time I opted to rebuild and use an M Tech with a view of getting it to run cooler. Of course I checked all the top end and was advised to go for a wider ring gap? and a bigger squish. I was all over the place with the settings on the M Tech but it ran OK but I seemed to be hitting a brick wall on revs. I was trying to run at 17-15 on full chat but had problems dropping out of the pipes power band changing from 3rd to 4th. so the M Tech came off. It was then that I noticed the spitback as it was a sod to restart.
Image
The cream deposits are from the spitback on my rear runner after a very short ride with no rubber on.
3 weeks ago I rebuilt the top end with new rigs going for a smaller ring gap. and the squish was 1.2. The spit back was unchanged. It was an unmolested barrel with no porting.
Any ideas guys or does anyone have any info about measuring the port timings. I did notice the piston goes down about 4 mm below the exhaust port, I expected it to be level with the bottom edge.
Last edited by Monty on Sun May 04, 2014 6:03 pm, edited 1 time in total.

mick1
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Sun May 04, 2014 6:02 pm

I've had issues with jetex carb's in the past and would consider replacing the carb with a Dellorto. I agree the piston should be level with the exhaust port but i'm unsure as what the effects of it being 4mm lower will be.....

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Monty
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Sun May 04, 2014 6:18 pm

I think the vid link works without the youtube tags.
I understand the Jetex has a bad press but the 22 mm carb has been fine for 3 years. I have never got anywhere with the 26mm but is exactly the same with no other changes. Im thinking I either have a hell of a lot of blow back into the rear of the piston (thats coming out at low revs) The blow back idea is why I replaced the rings. The piston is the one removed at the time I spotted the plating, (to be honest the thought of spending another 100 quid on a new piston and the fact that my guy was not open, I opted to go again with the old piston) it had no damage other than the rings and had 2000 miles on it. its the same crank, with only a standard bottom gasket and no head gasket as the head is top hatted. So other than the fact it has been to Somerset and back it should be as it has always been.

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coaster
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Sun May 04, 2014 6:43 pm

Hmm looking at your vid, I'm thinking that may be a float related issue i.e. fuel at the float valve not shutting off or fuel level too high. I thought that spit back was more of a 'cloud' of vapour rather than a drip :?

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Monty
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Sun May 04, 2014 6:51 pm

The float on a jetex is pretty much not adjustable. And its a jetex needle not the slightly shorter Dellorto one. (A short one would make it worse) Its the same on both carbs and I have tried adding a blob of solder onto the back side of the needle to close off a tad earlier than the standard red tip. its the same on both carbs and yes its like a dripping tap. Its also milky like its emulsified. see the runner. Last week I drained the tank and refilled with the same results.
Last edited by Monty on Tue May 06, 2014 8:37 pm, edited 1 time in total.

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Monty
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Tue May 06, 2014 8:35 pm

Hope Im not boring the pants off you...
Top end off again, the head has a waxy? deposit
Image
Image
When touched it shows a drop of moisture? After the head had been off for a while it dried up somewhat
All gaskets bottom head and inlet show no signs of air leakage.
Image
Piston at BDC seems OK its not well below the exhaust port.
and yes the piston is the right way up
Image
I have checked the ring gap at different positions down the bore, its .030 top and bottom with .035 just above the exhaust port (measured at points without any ports)
I had done an oil change within the last 6-8 weeks so drained the gearbox to see if all I had put in came out. it was within 20 ml. It was not smoking so Im happy the seals have not blown.
I have taken a sample of fuel into a clean container. How long do you have to let it settle for if its water/ethanol mix. It was a fresh tank full last week after I drained it just in case.
Im fitting an old cast 150 kit to check the crank case and timing again as I am running out of things to try other than going for a deloro carb. Something I dont want to do if I can help it. I have an aversion to needles and rubber.

cgt75b
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Tue May 06, 2014 8:59 pm

Hello Monty I have a known good Jetex carb if you want to try that :D

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Monty
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Tue May 06, 2014 9:21 pm

Before this all started I would have sworn by mine. If you are local N West I would happily take you up on your offer. I know they get a lot of flack but I like the simplicity of them. If I can prove its carb related I would happily buy another one but I cannot get my head round the emulsification, the pici of the rear footboard looks like a seagull has had a dump on it.

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coaster
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Tue May 06, 2014 10:28 pm

When you say you drained the tank, would it be likely that there was still some residue left in the tank? Maybe the water sits on top of the fuel and some got left in the tank? Just thinking out loud here, oil does emulsify when it's mixed with water and air.

belly
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Tue May 06, 2014 10:29 pm

Don't know about the carb but seems to me that your port timings may be out as piston shouldn't really be below level of exhaust port

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