propane problems

[SJscouter]

Iv go a sbc that is pretty mild with an Impco 425 model E on it. Iv had it for a few seasons but have never had it running right. Its always been slow. No power and id be lucky to get the rpm's over 2500. Its also consuming large amounts of fuel. From loon lake to the springs ill use a whole tank. 8 Gal. which before propane I could do the whole trail both ways on less than 10 gal. of fuel. I pulled the top screws out of my mixer to check things out and now better understand how the fuel mixture is made, but it doesnt seem to make much difference where that screw is, still running like crap an consuming lots of fuel.
Iv also messed with the timing and had no luck. Iv looked for vacume leaks and found none. Iv looked for propane leaks on the line and found nothing as well. Im at my wits end with this system and about to either scrap it and buy a new kit from got propane or get a tbi set up.

[GMCJocephus]

How much rpm's were you getting out of the motor when it was gas?
Have you switched to a colder spark plug?
Is the vaccum advance still hooked up?

These may seem like dumb questions but I'm not really understanding why your having this problem....

[SJscouter]

Originally Posted by GMCJocephus

How much rpm's were you getting out of the motor when it was gas?
Have you switched to a colder spark plug?
Is the vaccum advance still hooked up?

These may seem like dumb questions but I'm not really understanding why your having this problem....

On gas, i could hit 6k if i wanted.
never switched the plugs but this is a larger issue than that.
Ill double check the vac. advance but im pretty sure its good.

[SJscouter]

vacuum line runs off of the front small port on the throttle plate then T's to the distributor and the vacuum lock off.

Tomorrow Im gonna pull the mixer and the Model E and tear them down. With the amount of propane Iv been going through there has to be an obvious issue.

[GMCJocephus]

Originally Posted by SJscouter

vacuum line runs off of the front small port on the throttle plate then T's to the distributor and the vacuum lock off.

Tomorrow Im gonna pull the mixer and the Model E and tear them down. With the amount of propane Iv been going through there has to be an obvious issue.

I would get rid of the T, and run the vacuum line from the throttle plate to the lockoff before I tore down the the mixer. I had somewhat similiar issues with mine. talked to a few guys on here, they suggested that I don't run the vacuum advance, and it has done fine ever since

[SJscouter]

Originally Posted by GMCJocephus

I would get rid of the T, and run the vacuum line from the throttle plate to the lockoff before I tore down the the mixer. I had somewhat similiar issues with mine. talked to a few guys on here, they suggested that I don't run the vacuum advance, and it has done fine ever since

interesting, Ill try that today
Thanks for the help

[SJscouter]

forgot to mention, Last time i was leaving fordyce, Coming out of the committee crossing area once I was on fire roads I could bairly get my truck to move, I messed with the mixture screw and not much helped. the propane hose on the top of my tank was all frosted over which makes me think its just gulping the fuel down and giving me a whole 40hp.

[SJscouter]

I pulled the mixer and everything inside there looked good, all the diaphragms are new and look to be silicone. The evaporator was a different story. I pulled the coolant side first braking a few of the rusted in screws to find that about half of the passageways were completely plugged with crud. I cleaned it out and pulled the other side apart. Found a little spot in the large rubber diaphragm that had multiple holes. The inside of the thing was pretty oily and messy.

Im still not 100% clear on how these systems work but it seems like the evaporator is somewhat of a regulator too? Because the model E was in such bad shape Im going to order a new one with silicone parts.

Could this have been my problem???

[kyky777]

how much timing are you running on a healthy smallblock we switched to propane had to actually advance the timing to 24deg.

[azcagiva]

Pull the air valve out of the 425 and look at the bottom of the silver cone. See if it has the number 51 or 19. If you have the 51 that is why you are using too much fuel, it is for a feedback system that is controlled by a small computer. No computer= pig rich. If you have the 19 then look down into the carb and make sure the hole the cone rides in is still round.

You can get a new #19 air valve if you have the 51, if the hole in the carb is wore out you will need a new carb.

-John

[SJscouter]

Originally Posted by azcagiva

Pull the air valve out of the 425 and look at the bottom of the silver cone. See if it has the number 51 or 19. If you have the 51 that is why you are using too much fuel, it is for a feedback system that is controlled by a small computer. No computer= pig rich. If you have the 19 then look down into the carb and make sure the hole the cone rides in is still round.

You can get a new #19 air valve if you have the 51, if the hole in the carb is wore out you will need a new carb.

-John

Right on ill check this afternoon, I remember someone saying something about that hole before and I looked at that a while back and it has a tight seal in there.

[SJscouter]

Originally Posted by kyky777

how much timing are you running on a healthy smallblock we switched to propane had to actually advance the timing to 24deg.

I think its set at 12/36* seems to be what most guys are running

[altfuel1991]

Originally Posted by SJscouter

Iv go a sbc that is pretty mild with an Impco 425 model E on it. Iv had it for a few seasons but have never had it running right. Its always been slow. No power and id be lucky to get the rpm's over 2500. Its also consuming large amounts of fuel. From loon lake to the springs ill use a whole tank. 8 Gal. which before propane I could do the whole trail both ways on less than 10 gal. of fuel. I pulled the top screws out of my mixer to check things out and now better understand how the fuel mixture is made, but it doesnt seem to make much difference where that screw is, still running like crap an consuming lots of fuel.
Iv also messed with the timing and had no luck. Iv looked for vacume leaks and found none. Iv looked for propane leaks on the line and found nothing as well. Im at my wits end with this system and about to either scrap it and buy a new kit from got propane or get a tbi set up.

It sounds like you have more than one problem.If you got the model E corrected,take a look at the timing. You want 30 degrees@2500rpm(base&centrifugal).On some engines we run as much as 18 base.If you use vacuum advance connect it to the mixer for port vacuum, limit it to 10 degrees additional. If the distributor is difficult to recurve we have a dual curve timing module to change the timing electronically($150.00) that works well. Check lever height in the vaporizer also.You can call me,877-403-7827 . We have been in business twenty years.I am a new vendor.

[SJscouter]

Air valve is a #19

[azcagiva]

The model e should have the lever set to where the pin is just below the edge of the body. No gas should come out of the vaporizer unless there is a vacuum pulled on it or you push the primer button. They used to make different springs for the model e arms. The orange one was softer so it made it run a little richer, the blue one is the one you want. If they have been in there for awhile it is hard to see the color on the spring.

If the vaporizer is working correctly and the small slotted screw does not effect the idle it is most likely due to the mixture cone seat being worn causing extra fuel to be pulled during idle.(assuming the idle diaphragm is intact) In the old days impco had a small teflon seat that you could replace, no such luck anymore. If the seat is wore that will make it rich everywhere too. The easiest way to fix it is a new carb. I have machined some and pressed in a new bushing, but took some time.

Another way to adjust the timing is to use a vacuum gauge. Adjust the initial with no vacuum advance to the highest manifold vacuum and then retard it so the gauge reads 1" less than the peak. Try to keep total under 36ish. I have had luck with this on older trucks where the balancer has spun and moved the timing marks.

-john

[SJscouter]

thanks for the input. I got to talk with altfuel1991 today and he seems to think the issue was my evaporator, which was pretty thrashed. Im gonna order one from him and start with that. If I can get it tuned better Ill see how it goes on a few trips. If my rig still gulping the fuel then I know its the seat where the air valve slides (which seemed pretty tight)