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View Full Version : carb piston keeps dropping... no vroom vroom



jbarry
04-18-2006, 06:08 PM
1980 spitfire...
the carb in question is the stromberg 150 CDSE.
I did the home rebuild, and it started out fine, but seems to run way too rich... the piston keeps dropping too low- the the point where it stops running all together...I cannot even start it without manually lifting it up slightly with a screwdriver or something...
what would cause this?
I replaced the needle and adjusted the float today...... I have the needle adjusted so it is flush with the piston...
(note: this happens regardless of where I adjust the needle to)

Any ideas?

Thanks in advance!!!

James

bobh
04-18-2006, 06:29 PM
Is the diaphram damaged?

jbarry
04-18-2006, 10:10 PM
nope... it was replaced with my little rebuild in a box... although I'm tempted to put a little sealer on the bead...

jbarry
04-18-2006, 10:12 PM
are all diaphrqam's created equal?

I wonder if I got a cheapo one... the rebuild kit came from victoria british, maybe I should just order a new diaphram from spitbits or something...

04-19-2006, 04:56 AM
[ QUOTE ]
are all diaphrqam's created equal?

I wonder if I got a cheapo one... the rebuild kit came from victoria british, maybe I should just order a new diaphram from spitbits or something...

[/ QUOTE ]

There are rebuild kits and then there are real rebuild kits.
What you got was near the bottom of the barrel. Check with one of the professional rebuilders such as Joe Curto or Gary Martin or your above mentioned SpitBits. I have several boxes of the same type of kit you are referring to sitting on my shop bench, they really are pretty much junk.

Bill

piman
04-19-2006, 07:43 AM
Hello James,

why do you say it's rich, if you need to lift the piston (that will enrich the mixture) to start it? I would doubt that the diaphragm, cheapo or not, is the cause of your problem. Have you made any adjustment to the jet?
The other thing I would carefully check is your ignition settings and plugs.

Alec

bobh
04-19-2006, 09:21 AM
If the diaphragm is damaged, there will not be enough vacuum to raise the air valve. If the air valve is inoperable this will cause a rich condition. Engaging the choke at startup will aggravate the situation.
Having to manually raise the air valve indicates there may be something wrong internally.
James,
How did the engine run before you rebuilt the carburetor? Was there a problem with the carb? Tell us more about the before and after symptoms. I'm sure the collective braintrust of this forum can help to isolate the cause of your problem.

jbarry
04-19-2006, 10:28 AM
[ QUOTE ]
Hello James,

why do you say it's rich, if you need to lift the piston (that will enrich the mixture) to start it? I would doubt that the diaphragm, cheapo or not, is the cause of your problem. Have you made any adjustment to the jet?
The other thing I would carefully check is your ignition settings and plugs.

Alec

[/ QUOTE ]
it seems to not be allowing hardly any air in, so when I lift the piston more air gets in too... also... I can pump the gas as much as I want to try to increase rpms...but it only seems to make it worse... it sputters and evently kills... but if I stick a thin screwdriver in there and slightly lift the piston... it roars to life.

sometimes when I turn off the engine, there is a loud backfire (sounds like a real gunshot, much to my neighbors' dismay- hehe)... as if there was a bunch of unspent fuel in the exhaust system.

the back fire has not happened the last few times ( since I readjusted the float, and put in a new needle)... then again, it has only run 2 or 3 times since then.

My brother has a weber downdraft on his 1500 midget... so I threw it on there to try it out a bit... it ran- sort of... but the cat got so hot it looked like it was about to start glowing... the paint on the inside of the engine bay started smoking (not just the usual oils, etc...)
He didn't want me to fiddle with his settings for his car, and I figured it would be futile to continue without making adjustments so I gave back his carb...and went back to work on the stromberg.

at this time I had not yet changed the neede, or adjusted the float... so when I put the stromberg back on and started it... gas was pouring out the air inlet- (where the air cleaner mounts)... it was coming out at the rate of about 3 drips/sec.... that looked like trouble brewing so I killed the engine before making big flames everywhere and went back to the drawing board. now he needle is swapped with a new one. and the floats adusted..

I've checked the float- it looks fine... not a drop of gas in it. Also tossed in in a bowl of gas, and it floats great too.

jbarry
04-19-2006, 10:38 AM
here's something I thought was weird...
I ordered the new needle from spitbits... (a 45N)
this is the one which was originally in my carb... and the one I pulled out is a 45N...

but the new 45N is about 3/16" shorter than the old one.... weird, eh?
I called the guy at spitbits and he said it is the right one and to use it anyway- it will just make the piston sit a little lower...

I don't think this is the problem because it did seem to run a little smoother(when it did run) with the new needle over the old.

jbarry
04-19-2006, 10:43 AM
maybe I should go to a dual carb setup like this and be done with it...
https://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8056152537&sspa gename=STRK%3AMEBI%3AIT

(auction # 8056152537- it ends tonight)

trrdster2000
04-19-2006, 07:19 PM
jbarry, here's a guess, you are working on the wrong end of the car, I think you have a stopped up muffler or some other restriction in the exhaust. You can't get air in if it doesn't clear out. Hope this will give results. Wayne

vettedog72
04-20-2006, 03:36 AM
3/16" is a huge difference concerning needles. I think you have a needle and or jet problem if you have eliminated the diaphragm as a problem. If you have a significant difference in needles, it may be your jet has been changed by PO as well.

jbarry
04-20-2006, 10:01 AM
[ QUOTE ]
jbarry, here's a guess, you are working on the wrong end of the car, I think you have a stopped up muffler or some other restriction in the exhaust. You can't get air in if it doesn't clear out. Hope this will give results. Wayne

[/ QUOTE ]

That would be awesome... not too likely though... I had a new exhaust system put in from the cat back in January... (& it ran fine for a while...)

jbarry
04-20-2006, 10:05 AM
[ QUOTE ]
3/16" is a huge difference concerning needles. I think you have a needle and or jet problem if you have eliminated the diaphragm as a problem. If you have a significant difference in needles, it may be your jet has been changed by PO as well.

[/ QUOTE ]
does this carb have replaceable jets? maybe this is my problem... I don't remeber one coming with the kit... I did replace the brass gas valve in the bowl- is this what you're referring to?


here's a correction... the carb kit I used came from Moss- not vic. british... probably no difference though /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/confused.gif

jbarry
04-20-2006, 12:16 PM
[ QUOTE ]

There are rebuild kits and then there are real rebuild kits.
What you got was near the bottom of the barrel. Check with one of the professional rebuilders such as Joe Curto or Gary Martin or your above mentioned SpitBits. I have several boxes of the same type of kit you are referring to sitting on my shop bench, they really are pretty much junk.

Bill

[/ QUOTE ]

Anyone else have experience with Joe Curto's quality?
I can send the carbto him and have it overhauled for $200...
I'm just getting eager tosee this back on the road... and still not sure what the issue is...


I don't think it could be something else in the engine... it has new cap, rotor, plugs, wires, pertronics, ... is timed @ rcommended spec...

here's a question... the kit I used did not have a replacement bipass valve diaphram. the old one looked pretty old, but undamaged.. Would this cause these probs?

jbarry
04-20-2006, 12:31 PM
I called and talked to the guy at joe Curto's... he said most carb kits are of relatively equal quality, but that some just come with more bells & whistles...

in his opinion he thinks my choke is messed up, so I will tinker with that for a bit.

Does anyone know if this carb has a manual choke conversion kit available?

04-20-2006, 12:45 PM
You might want to poke around somewhere like here to see if it gives you more ideas:

https://www.triumphspitfire.com/carbs.html

jbarry
04-20-2006, 01:37 PM
https://www.paulbunyan.net/~jasko/choke/

found this...
I'll tinker with it this weekend and let you know how it goes.

jbarry
04-26-2006, 06:02 PM
I replaced the bipass valve diaphram, and also installed a manual choke kit... it still kills after heating up and for whatever reason the engine keeps overheating...

any ideas?

bobh
04-26-2006, 07:31 PM
James,
How did the engine run before you rebuilt the carburetor?

The overheated catalytic converter is another sign of an overly rich condition. When the cat gets up to operating temperature, and unburned fuel is exiting the engine into the exhaust system. The fuel will ignite when it hits the core of the cat.
You say the engine is overheating. What temperature do you see on the temp gauge?
Based on what you have said, these are my conclusions;
Your carburetor is way too rich.
That is why you see gas coming out of the face of the carb.
Seeing the RPM rise when you manually raise the air valve is an indication of a rich condition. Raising the piston allows more air to enter the intake. This allows more of the gas to burn and the RPM increase.
The overheated cat is another indication of it being too rich.
The exhaust system is overheating, causing the paint to smoke in the engine bay. (I don't know the temp gauge reading, this reading would help to know if it's the engine or the exhaust)

There is something very odd about the needles. I can't comment on the reason for the difference in length. Unless the previous owner installed a different carb, or replaced some of the internals.

Is it possible that the carb is not the original?

Did you replace the fuel pump? If so, did you replace it with an electric pump?

I suggest you check the following;
1) You may have melted the core of the cat when it overheated. Remove it and check. If it is damaged, and you fix the problem in the carb, you will still have problems when you try to run the engine because the exhaust system will be clogged. This is in line with what trrdster2000 mentioned in his reply.
2)Remove the float bowl and check the setting. If the float is not set correctly. When the fuel pump is pumping, the float is not closing the needle valve which allows excess gas to pass through the jet into the intake.
If you have a mechanical pump with a manual priming lever. Try pumping it while someone lifts the carb piston and watches to see if raw fuel is coming out around the jet. I'm not sure you can pump it fast enough to see gas leaking. However, since the engine is not running, therefore not sucking the fuel into the intake, you may be able to see any excess gas that is flowing out of the seat.
3) Check the fuel pressure. If you have an electric fuel pump, or a new mechanical pump your fuel pressure may be too high. Too much pressure can overcome the float/needle valve and force extra gas into the jet. You can install a fuel pressure gauge in the fuel line. Speed shops sell them for around $20, add a couple of dollars for some fittings. If the speed shop doesn't have the fittings call an industrial supply house or hydraulic hose supply house. The fuel pressure is fairly low for these carbs. Use a gauge that reads something like 0 to 10 PSI. You don't need one that reads 0 to 100. The pressure you want to read is around 3 pounds (? check the manual)
4) Check the needle valve. Make sure it is closing when the float reaches it. Also check to see that the needle valve is fully seated and sealed. Even if the needle valve closes properly, gas could get past the valve body if the seal is not good or the threads are damaged.
5) If none of this helps you may be better off sending the carb to one of the professional shops mentioned above. Curto has a good reputation. I believe TR6Bill used Gary Martin to build his triple carb setup. (Is that correct Bill?) There is also a rebuilder in Ohio named Jeff Palya.
BOBH