I have a SBC 350 that is mildly built. I don't know they exact specs on it but I do know that it is
30 over
Cam-unknown
camel hump 202 heads
It currently has a Holley 750 double pumper on it and runs good. I'm wanting to convert to propane but I don't know if a 425 mixer will be enough. What are your thoughts?

its enough

have more or less the same set-up except in a 327 flavor...

425 will definately handle it, and you'll wonder why you ever mucked with a carb for wheelin...

put it on 'pane and let it rip!

I put the pane on a few nights ago but it’s not running yet. I think I have a timing issue. The engine spins over fast briefly and then the starter will slug down and then stop like the battery is dead…but still has 12 volts. My truck was previously a bitch to crank on gas and it seems to be the same way now. When the motor was cold I pretty much had to dump gas in the carb and then cover it with my hands to get it to crank. I have an impco 425/model E/ vacuum lockout. I think that I'm going to switch to an electric lockout. I used the base plate of my old double pumper...which I shouldn't have done.....I'm running a elderblock victory intake that has no vacuum ports on it. My base plate only has two vacuum ports. I'm using one for the timing advance and the other for my Brakes. It doesn't seem like I have enough vacuum to open the lockout.

Any advice to get it running? I know I need to get a high torque starter.

All new parts or used junk?

Do you have a primer? It normally takes some cranking to start without one, since the propane has to be vapourized, then travel along the big feed hose to the mixer, then down the intake port before it enters the combustion chamber.

Sounds to me like your battery is pooched, and simply has no capacity. That it shows 12V after cranking doesn't mean much, just that it recovered once the starter stopped. Also, you might have an issue with the battery cables or the brushes in the starter and what not.

Fix your electrical.

Also, if you fear you don't have enough vacuum, buy a hand vacuum pump (for diagnostic purposes) and use it to trip the lock-off. You can rule out if that is your problem right there (I doubt it is).

If the parts are used, or have been user overhauled, there could be other issues.

The battery has been through hell so I will have it tested and I see if I can exchange it for the 4th time.

I'm going to replace the starter with a hi torque unit

The cables are fine...all new and done correctly

The whole propane set up is used but was tested on the POs truck before I bought it.

I've talked with a few people and they said the starting issue is more than likely the timing. They said if it's too advanced or too retarded then the motor would be hard as hell to crank...I don't remember which. I'm gonna try to find someone local to work on it...I'm tired of fucking with it.

I don't buy the timming deal, even if it was set at 0 your starter should still turn the engine over. I'm guessing you have a bad stater, or a bad connection. Take the starter and have it checked at a autoparts store. If you think the timming is the issue pull a spark plug and turn the engine over by hand until you are on a compression stroke and just before the cylinder gets to the top stop. Check to see if the rotor is pointing to the correct wire on the cap. That should get you close enough to start the engine.

I guess the compression has weakened the starter. I'm going to order one fo the 3hp mini starters off ebay and see how it does. Myabe the shitty starting was because the engine wasn't spinning fast enough?

425 feeds my 454 to 6000 rpm. Mine starts quick and runs great every time. Make sure you have a good ignition. I run GM HEI with a MSD box and no vacuum advance. Electic lockoff starts quicker than vacuum, been running mine for 2 years no problems.

425 feeds my 454 to 6000 rpm. Mine starts quick and runs great every time. Make sure you have a good ignition. I run GM HEI with a MSD box and no vacuum advance. Electic lockoff starts quicker than vacuum, been running mine for 2 years no problems.

I'm running an HEI with vac advance. I'm going to switch to a electric lockout and I should order the new starter tomorrow.

You sound like you like to guess at stuff, but not do anything.

You 'guess' your starter is fucked.

You 'guess' you don't have enough vacuum to open the lock-off.

You 'guess' your timing is wrong.

You've been through 3 batteries, yet you're going to order a new starter rather than test the battery first... You think there isn't enough vacuum to open the lock-off, but rather than hand pumping it to verify that the lack of vacuum is a probable issue, you're just going to order an electric one. You think the timing is off one way or another, so it's hard to start (BS anyways), but rather than waddle out there with a wrench and a screw driver to check it, you just bitch about it on here.

How about you just fucking go out there and try some shit? This is NOT hard stuff. Jump the truck with a known good battery to rule out the one you have. Get a vacuum pump to try the lock-off (I doubt that's an issue). Go check the fucking timing... Hell, if the starter IS fucked, I bet you could pull it apart and clean it up so it would at least work well enough to get a start out of it.

You also never answered if you had a primer.

If your worried about compression, pull the plugs & test it.

Your description of it turning over is vague.

Get the starter tested & go from there.

Offer a buddy a 6 pack to come over & drink & tinker.

Well since I was doing too much guessing...I did some testing tonight. I check checked the timming the timing and it was dead on advanced just a bit. I verififed that the vaccum lockout was opening. I held my hand on it while I turned the motor over. Even with it spinning slowly I could feel it open. Then the starter finally gave out. I will be ordering a new one tomorrow.
The 3 battery statement was from the past year and a half. I have gotten my duralast gold replaced 3 times. The last time was my fault because the chevy one wire was putting out 18 volts and cooked the battery (when the truck had a 22r).

Yes it has a primer

The truck runs like a champ now....

I replaced the starter, battery, set it timming, and still no go. A buddy of mine came over and we found that it was the tank valve.....We had some flow but not enought. We tripped the ball a few times and then it worked fine after that.

My problems continued to bring the suck. I could start the truck off either but it would never even hit of propane....yes I primed it. One it was started then it would run fine off propane. I could leave it runng for 30 seconds or 15 minutes but if I shut it off it wouldn't crank back. I took the mixer apart last night and inspected/cleaned the diaphrams. Surely this would be the cure all to my problems....FAIL. Then I got pissed and put the Holley back on. It took two pats of the gas it it cranked easily. I shut the truck off and it cranked back with ease. I hate my truck.

budy of mine has exact same issue with his pane setup on a new rebuild motor. Very hard to start, and once started run's like a champ.

Worn out propane 425. Installed the one from my truck and all is well.

Even went throught the same issues with starter, battery, timing before we started tearing parts off my truck to isolate the propane component.

Rebuild your 425 and model E, and I'll bet you're pane problems will be solved.

Or get new junk.

Just because it worked on your buddies, doesn't mean it'll work on yours. My firends truck run/started just fine with his pane setup on on the tired 350... now with a 350hp 350ci, it gave him fits!

My 425/E set up worked OK when I first installed it.

I got it from the local JY. Before install I took everything apart, cleaned them & put them back together.

Ran it like this for one summer.
A year ago I rebuilt it with the rebuild kits, got rid of the vacuum lock off, I replaced it with electric solenoids at the tanks...(can have both tanks open without them equalizing, and I can hit a switch to go from one tank to another once one is empty).

It runs much better after the rebuilds.
I have no choke, so it does take a bit to start & then warm up but not much (about 4-5 attempts to start, which I think is caused by it propane getting to the engine/expunging propaneless air from the engine).

Have you even tried adjusting the idle mixture? I've had this make a huge difference. Vacuum leaks can make the exact symptoms you're describing as well and is more likely the problem. I've had 2 BBC trail rigs on propane, both running 425s and Model Es. Both of mine start and idle like they're fuel injected even in 0 degree weather. Don't give up on it yet.

Used propane parts suck. The 425 has wear parts that can't be rebuilt. I installed all new parts (425-M6-elock off) and triple checked for vacuum leaks and it fired instantly the first time and has been running flawlessly ever since. Vacuum leaks will ruin your day. IMO the M6 is a far better regulator than the model E at sustaining higher HP demands.

I had a friend put the propane set up on his truck and it started easier and faster than his own set up did. He used a different base plate but I didn't see any vacuum leaks on mine.

I have a vacuum line going to my brake booster. I noticed while the truck was running that the bakes were terrible. Could it be pulling vacuum through the brake booster?

I need to shim the stater and cap that vac port off and I'm going to try cranking on pane again. This truck is really pissing my off.

Mine did the exact same thing yours has. It was the idle mixture, like fmstruck said. Screw it all the out and turn it over a couple of times, then do a half turn in and turn over. Keep doing the half turns in and turning it over until it starts. Then you will have to adjust from there on how your rpms look. I went just pane, so I blocked all my vacuum hoses except the booster, then advanced my timing as far as I could, But once you advance your timing you will have to adjust your idle screw again in or out depending on where your rpms are setting. Cold idle I have mine around 2500, Warm around 900. If you want to rebuild your kit it will cost you $20 per component. Very easy and it comes with instructions. Call acme and ask for Dave at 507-345-4000, very knowledgeable. If the truck started with gas before you switched to pane then it is the pane. I know guys that do not adjust there timing at all with pane.

The truck is in the shop right now gettin a my little issues worked out with the carb on it. Once I get it back then I'm goin to have someone else put the propane on it. I'm sick of working on it. I also bought a 3hp mini starter off ebay and.....

I bought one for a 168 tooth flywheel. I put it on and it's ridding on the edge of the flex plate teeth.:shaking:.

A year ago I rebuilt it with the rebuild kits, got rid of the vacuum lock off, I replaced it with electric solenoids at the tanks...(can have both tanks open without them equalizing, and I can hit a switch to go from one tank to another once one is empty).



This is a GREAT idea!
Thanks!

:beer:

To save some $$$, you can get by with only 1 solenoid.
Put a 1 way check valve inline on one tank (propane can go out, but not in).
The second tank has the solenoid which keeps propane out & in.
Once the first tank is empty, you can hit the switch.