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Solex carb jetting

BoyToys

BoyToys

Well-known member
Super Patron
For those still using the stock Solex on their Ford V4 powered Imps, looking for feedback on what you're using for pilot jet sizes. Running at 3600 feet elevation.

I've never been happy with the engine performance...will bog down starting out from a dead stop if throttle is fed too quickly. Otherwise idles fine but needs to be at 2000-2500 rpms when cruising in order to have any power. As a result I have to operate with the rear end in 1st gear and can use only 1st and 2nd in the tranny. I just lived with it last winter.

My Solex came with a 45 pilot. I just recieved a set of 5 ranging from 45 to 65, and yesterday plugged in a 60. It seems to have helped and I was actually able to run in 3rd gear up front as long as I kept the rpms up...but not from a dead stop.

Still seems that it's running mostly on the main jet at higher rpms. Little bottom end power to speak of. This after a total carb rebuild and cleaning. Valves all adjusted, ignition timing set to 6° BTDC. Should probably check compression.
I'm just about to spend the cash and go Weber.
 
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I have a few spares laying about. Ill do my best to what the jet sizes are.

We are at 745 to 2900 fas
 
BoyToys said:
For those still using the stock Solex on their Ford V4 powered Imps, looking for feedback on what you're using for pilot jet sizes. Running at 3600 feet elevation.

I've never been happy with the engine performance...will bog down starting out from a dead stop if throttle is fed too quickly. Otherwise idles fine but needs to be at 2000-2500 rpms when cruising in order to have any power. As a result I have to operate with the rear end in 1st gear and can use only 1st and 2nd in the tranny. I just lived with it last winter.

My Solex came with a 45 pilot. I just recieved a set of 5 ranging from 45 to 65, and yesterday plugged in a 60. It seems to have helped and I was actually able to run in 3rd gear up front as long as I kept the rpms up...but not from a dead stop.

Still seems that it's running mostly on the main jet at higher rpms. Little bottom end power to speak of. This after a total carb rebuild and cleaning. Valves all adjusted, ignition timing set to 6° BTDC. Should probably check compression.
I'm just about to spend the cash and go Weber.
Click to expand...
I don’t know much about Solex carbs but it sounds like a leaky accelerator pump or needle/float issues. My thought is it’s really heavy on fuel and is flooding g possibly?
Does the exhaust give you any clues? Does it seem normal or does it smell like gas (too rich)?

Keep us posted! I love my Weber! Super snappy throttle and simple!


Keep us posted!
 
Idaho IMP said:
I don’t know much about Solex carbs but it sounds like a leaky accelerator pump or needle/float issues. My thought is it’s really heavy on fuel and is flooding g possibly?
Does the exhaust give you any clues? Does it seem normal or does it smell like gas (too rich)?

Keep us posted! I love my Weber! Super snappy throttle and simple!


Keep us posted!
Click to expand...
Accelerator pump brand new, as are the float needle and seat. Float height is non adjustable basically and is dependant on the gasket thickness (hard to explain). Does not starve for gas at higher rpms/loads. Does not smell rich and plugs if anything look to be a tad lean.
My first thought was that the accelerator pump wasn't injecting enough fuel resulting in a lean transition off idle. Throttle plate opening set to spec and mixture screw adjusted to best idle. Seems as though when coming off idle and the throttle plate exposes the delivery port it will stumble and/or cough and die if I feed too much throttle too fast.
Last winter I ran with the 45 pilot jet it came with, and 40 is the smallest size you can get....so just the other day I swapped in a 55, then a 60. Helped somewhat with the transition but still seems to lack any decent power under load while crusing unless I keep the rpms up at 2000 or beyond.
 
Might the issue be the engine timing not advancing under load maybe due to a vacuum leak or faulty diaphragm?
 
Looked up Symptoms of a Vacuum Advance Failure and found things that match your engine's behavior description. In a previous post you said the timing was 20 BTDC when you got the machine. If the timing advance has issues, the previous owner may have set it that way to get better performance at mid- to upper-level RPMs and not to compensate for elevation. FYI: I'm not a mechanic so I might be entirely wrong here.
 
zspryte said:
Looked up Symptoms of a Vacuum Advance Failure and found things that match your engine's behavior description. In a previous post you said the timing was 20 BTDC when you got the machine. If the timing advance has issues, the previous owner may have set it that way to get better performance at mid- to upper-level RPMs and not to compensate for elevation. FYI: I'm not a mechanic so I might be entirely wrong here.
Click to expand...
Good points.If no vacuum advance due to a leak or diaphram issue, performance would be dependant on mechanical advance that wouldn't kick in until rpms are substantially higher.

I had forgotten that when I first checked the timing it was way advanced and I moved it back to spec. At the time I did check the vacuum advance cannister simply by pulling the hose - plugging it - and attaching another hose through which I sucked with my mouth...and the rpms increased indicative of advance. So that 'probably' takes the cannister out of the equation but not a vacuum leak elswhere.

Checking the timing on these Imps is a real pain. Have to remove the right engine shroud, somehow affix a timing light beneath the alternator pointed to the pulley, then look down from the top of the radiator through a 1" gap. A helper would help but it's just me myself and I.

Next time I'm at my cat I'll try cranking in more advance and if that solves it, and check for vacuum on that hose. Need to find my vacuum gauge. I'm no paid mechanic, but have always wrenched on all my vehicles with very few exceptions.
 
I missed the 20 btdc post.

Take that into account. As well as which port it is hooked up to. I always look to see if the port is above or below the throttle plate. Easy to turn an advance into a retarder
 
redsqwrl said:
I missed the 20 btdc post.

Take that into account. As well as which port it is hooked up to. I always look to see if the port is above or below the throttle plate. Easy to turn an advance into a retarder
Click to expand...
True enough. There's only one port to connect to on my Solex so I have to risk the assumption that it's correct for providing advance once the throttle plate opens past that port.
Then there's always the fallback of using direct manifold vacuum, pros and cons to that approach.
I tossed out a new post yesterday on timing relative to my initial discovery of 20° BTDC...if you havent seen it yet.
 
After rebelting this aluminum frame.
Im motivated to finish rebelting those imp tracks!
20250604_152832.jpg
20250604_151122.jpg
 
Rainierrrrr....beerrrrr. Remember the old commercials? Happens to be my bev of choice, but of course being a Washingtonian.
 
zspryte said:
Time to revisit the jetting now that your power is restored?
Click to expand...
Yep, already went back to the 45 pilot that was in it originally. Without access to a CO gas emissions tester, will probably have to wait until this winter for a good run, shut down, and check the plug color. Old school, for old people.

I will add this: The following morning after setting the timing, I went out around 5:30 am, 43°F temperature, and lit her right up with about a 1 second crank. 1500 rpms, auto choke set perfectly, kicked her down to 1000 after a minute. All as it should be. Starting in the past took a lot more cranking, then very cranky until warmed up.
 
Cold morning, heavy wet dew in a hay field has been my go to tuning venue in summer.

And gravel driveways.

Glad your catching all these opportunities for improvement....

Giggle giggle
 
redsqwrl said:
Cold morning, heavy wet dew in a hay field has been my go to tuning venue in summer.

And gravel driveways.

Glad your catching all these opportunities for improvement....

Giggle giggle
Click to expand...
Heh...yeah. May need to run back up to the cabin, not that I need an excuse other than playing with the cat. Only 50 miles away. Unfortunately temperatures are soaring to triple digits in the next few days and I would prefer colder denser air somewhat more reminiscent of winter,
Lots of alfalfa grown around here. I can just hear the farmer's "comments" if I were to roar around in his fields, chasing the circle for that cold damp air. So much for the second cut....
 
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