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

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Monty
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Wed Aug 22, 2018 10:55 pm

Sorry guys not spotted this old post resurrected. What did I do, get pissed off with Lambretta’s basically. You can only take so many kicks in the balls without walking away for a bit. Changed to a 26 mm Dellorto. Wanted to run through the air box but not easy on a 26. So it’s got a breath sweet. Spit back/ dripping stopped. I think the work that Ant Tambs has done with pick up heights and different flywheel combinations prove the problems a lot of us have had are down to the ignition Kits currently on sale. You buy a new part thinking it will sort it and you just get more faults. The jetex I had run for years without fault other than holed pistons. :mrgreen: The Dellorto set up is a lot more complicated but it’s not on or off like a jetex. You can roll the power on and I’m not for going back to the jetex. Again Mr Tambs seems to have all the options. I like the move away from LT coils and pickups but not gone down that route myself. As I said I was so pissed off it’s been Sorned and covered up in the shed with me selling my Imola bike and buying a classic car to mess about with. just retired so got the time to spend a bit more time on the ruddy thing or sell it. I’m in the “it’s not costing me anything” so it can stay put. Playing with a 1969 Bond Equipe 2.5lt 6 pot. With parts being cheap compared with anything Lambretta. Everyone has jumped on the 800 for this 900 for that, too rich for my blood. Good Luck.

Daggs
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Thu Aug 23, 2018 7:26 am

[/quote]
I'm going to sell all 5x Jetex carbs and all my jets etc and buy a PWK instead see if that is more stable
[/quote]

How much do you want for the lot?

johnny650
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Sun Aug 26, 2018 5:03 pm

Monty wrote:
Wed Aug 22, 2018 10:55 pm
. As I said I was so pissed off it’s been Sorned and covered up in the shed with me selling my Imola bike and buying a classic car to mess about with. just retired so got the time to spend a bit more time on the ruddy thing or sell it. I’m in the “it’s not costing me anything” so it can stay put.
I'm rapidly getting to the same place myself.

its been 6x weeks and counting and I still haven't got my damn scoot working yet. They are unbelievably frustrating when they have intermittant faults and are so hard to diagnose.
I've swopped the 200cc for a 185cc which has been on and off more times than a tarts knickers (can I say that ?) :shock:

Yesterday I very nearly gave in and gave up. I too was going to put it in the back of the garage. I've missed all the Summer riding days on both the scoot and my motorbike and my other classic vehicle projects are now all 6x weeks behind .

One minute it will start and run perfectly the next it will start and die. Then it won't start for days then it runs for a few seconds and dies . Everything seems to be there , spark , timing, compression , oil-tight seals etc .
I have replaced the carb 10+ times with different jets etc and still nothing.

Yesterday I discovered a huge water bubble and some sediment in the fuel line ?? where the heck did that come from ?

I am so stubborn that I simply won't let the piece of %£$* beat me but its really stressing me out.
I'm even thinking of buying a £450 Muggy to bolt on .

johnny650
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Sun Aug 26, 2018 5:09 pm

Daggs wrote:
Thu Aug 23, 2018 7:26 am
I'm going to sell all 5x Jetex carbs and all my jets etc and buy a PWK instead see if that is more stable
[/quote]

How much do you want for the lot?
[/quote]

Daggs thanks for the offer I'm holding fire on the 6x Jetex until I get the Li running with a PWK and see how it goes . if its good I'll probably sell the lot and you can have 1st refusal. its a lot of gear and I can't see it going for much less than 3x figures to be honest

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Monty
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Sun Aug 26, 2018 7:31 pm

I'm rapidly getting to the same

One minute it will start and run perfectly the next it will start and die. Then it won't start for days then it runs for a few seconds and dies . Everything seems to be there , spark , timing, compression , oil-tight seals etc .
I have replaced the carb 10+ times with different jets etc and still nothing.

Yesterday I discovered a huge water bubble and some sediment in the fuel line ?? where the heck did that come from ?

I am so stubborn that I simply won't let the piece of %£$* beat me but its really stressing me out.
I'm even thinking of buying a £450 Muggy to bolt on .
[/quote]
I know the temptation is to set fire to the ruddy things but, in my case the problem started with carb spit back. It was more than that with neat fuel just dripping from the carb on tickover. You do all the normal things like checking float needles sticking but this just started on a tried set up so all the old comments about jetex carbs bad manufactured parts are null and void. I stuck it out trying to get the setup better. The spitback rolled into statorCDI and ignition all the above was as far as I’m concerned was the new BGM stator and CDI I bought. Yes we now know that pickup height makes a big difference, I worked that out after weeks of messing, I had a 10 degree swing on timing without a box of tricks. A spacer lifting the pickup helped but swapping the red BGMfor the Ducati one from my other bike solved the fault. The annoying thing was that the red CDI also worked spot on on my Imola so you are Not convinced. Then months later I’m pushing the Imola home and it starts and runs fine the next day. After 2 lots of the long walk home I ditch the red CDI and it was then perfect..
I said before as a jetex fan I finally went Dellorto but a Jetex should be simple to set up. I’m sure they have lean spots that can hole a piston normally when rolling off after a good hiding. But they should start and run. Ok main jet till boggy then back a couple. In your case I would want to see if your bubble is air or water. If it’s not new fuel drain it. Check your flow, taps are often full of s**t or even the rubber washer inside the tap that selects reserve are often full or black rubber crap. Reading Mr Tambs reports on no spark till 300 rpm all due to pick ups and lt coils would push me to electrics once the basics above are confirmed. Throw 100 quid at what you have on that side rather than tap on another kit. Then flog your surplus carbs to pay for it.
Ps check your pipes not blocked.

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chris2470
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Sat Sep 01, 2018 8:27 am

If the inlet timing is large >145° it will spit back at low revs, have you taken any readings to see exactly what you inlet timing is, it would be good to know. Also the Muggy has a boost port feed through a hole in it's piston at 12'O'clock, good idea check this is not protruding into the inlet a BTC.
I'd explore the possibility of shipping out what you have & fit a GT186 as it has a reed valve, spit back will be minimal.
Best Regards

Chris

johnny650
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Sat Sep 01, 2018 10:25 am

Monty apologies for not replying to your last post I am still not getting email notifications for some reason or other ?

Your tale of woe sounds like exactly the same as the one I have been through .

I had previously found some fine sediment in the fuel bowl so i removed the tank and thoroughly cleaned out the entire fuel delivery system replacing the filters an inline filter and fuel hose . I cleaned out the petrol can I use to mix my fuel and thought that I had eliminated any water or sediment but was incredulous to find it back again the other day.???

I have checked and replaced everything now so many many times that i'm convinced it has to be the carburettor at fault.
I am going to use a dedicated 2x stroke mixing/storage can and filter all my petrol from now on using some 190 micron paint filters . If any water gets in again I'm going to get the scoot exorcised !

I decided that it was about time I made detailed study of the Jetex delly SH1 carb and determined exactly how they function . I have been fighting them for the past 5 years and still didn't really know exactly how they work ,...even though they must be one of the most simple carbs on the planet..

I have always assumed (wrongly ) , that the mixture screw on these carbs controlled the idle fuel supply and was quite surprised to find that it doesn't !........the mixture screw controls the quantity of air AND fuel mixture to the engine !
Mixture screw really is a misleading description .

Idle air is supplied by a fixed jet at the mouth of the venturi and the fuel is supplied by the fixed pilot or idle jet that is fitted. Neither can be adjusted . Altering the mixture screw in or out varies the QUANTITY of that mixture of fuel and air .
To enrich the idle fuel mixture you need to fit a larger pilot jet not adjust the mixture screw

Now I'm wondering if the label on the Jetex carb carb stating 'A/F mix screw keep max 3/4 turn ' is actually where the screw SHOULD be set and we should be changing the pilot jet to lean or richen the idle mixture.

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Monty
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Sat Sep 01, 2018 12:36 pm

The air screw Mixture? is used for fine tuning. You have 3 jets Choke is a rich one and rarely needs changing its used to get it going from cold, once running and warmed up a bit choke can go off. if it dies your pilot needs to be looked at go bigger. If it wont start on choke or Bogs and cuts out on choke then maybe a smaller idel will help. get it running, ticking over you may need to adjust the long screw that lifts the slide and if anything have it ticking over slightly fast. some books say wind the air screw all the way in then back, now I have had new jetex carbs that say 3/4 turn and some books say 1 1/2 turns. If you can get it running as above you adjust the air screw till the revs start to race a bit. all the time blipping the accelerator to see how it rises and drops back down again. you are looking for the sweet spot. it will get lumpy if its too far in and smooth out as you wind it out. once you find the sweet spot you can adjust the long screw to slow the tick over down. it should rise and return to normal with a blip of the throttle. Main jet is for when you are going faster, if it bogs after 3/4 throttle you may be too big, turning on the choke at speed will bog it as its then way to rich. Forgive me if I'm preaching to the already wise man. Good Luck

johnny650
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Sat Sep 01, 2018 5:16 pm

Monty thanks for the response . i posted in the hope that peeps would question this and look at the idle mixture issue themselves.

there are a huge number of 'reliable' sources on the net that state that the mixture screw on the Sh1 /22 carb adjusts the idle fuel supply..........it does not ! They are all wrong ! They probably read the same source and simply copy pasted it

Adjusting the idle mixture screw in or out increases both air AND the fuel in a pre-set ratio.

Don't take my word for it....... or just accept what you've always believed .........get a carb out and feed some fine wire through all the orifices as I did and you will see for yourself that the mixture screw adjusts both the idle air and fuel mixture simultaneously.

It is impossible to separate either of them because the air and fuel for the idle mixture go to the same chamber where the pilot jet screws in, it is then fed to the combined idle orifice in the venturi .

johnny650
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Mon Sep 03, 2018 5:50 pm

chris2470 wrote:
Sat Sep 01, 2018 8:27 am
If the inlet timing is large >145° it will spit back at low revs, have you taken any readings to see exactly what you inlet timing is, it would be good to know. Also the Muggy has a boost port feed through a hole in it's piston at 12'O'clock, good idea check this is not protruding into the inlet a BTC.
I'd explore the possibility of shipping out what you have & fit a GT186 as it has a reed valve, spit back will be minimal.
Chris thanks for your suggestion sorry I didn't see your post mate.

The engine I have is a piston ported one not a Muggy . Its a Scooter Resto Indian cylinder kit apparently .

The ports are all exactly where they should be and I have posted a port map for this cylinder somewhere in this forum a few months ago. The piston is a standard 185 Indian jobbie so they should be perfectly compatible.

I now have great compression perfect timing and a good strong spark and I am certain that when I get a chance to flush the tank ,petcock and carb it should fire up and run perfectly.
The annoying thing is it has already done all that a few weeks ago . It made a blistering run up the village to the garage wherupon it refused to start after that .

I believe now that I have been using contaminated fuel .

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