I just bought a 79 bronco with a Fe on propane it has a impco mixer 250 in it I have in my collection of wierd stuff a duel mixer .2x 250mixers on a adapter to bolt on the 4 hole manifold will it cause more problems then its worth ? I have the whole system except the lines to the tank would the stock line pass enough gas to feed both mixers?how will I be able to check that I'm not overfueling or will it only pull what it needs to run? my experiance with propane is limited and varied but I have books!!!

 

What size motor? Can you get a number/letter off of the vaporiser? (ex model E)

Regards
Gasman

 

it's a 428 ford T-bird motor with some upgrades (cam,recurved ignition ,soon to get headers) I will have to check the motor for the model of vaperizor... I haven't gotten all the info yet on the motor,it's all new to me as I just got the truck a week ago and am still fineding out what everyone else has done.

 

What are your intentions with this truck? Is it a work-horse, daily driver, pro-mod race truck? Then how much do you want to spend?

Either way, that single 250 is way too small for 428 cubic inches. It's a bottleneck. That motor must suck for power the way it's currently set up.

It sounds like that oddball adapter is just a funnel to an already small intake opening... assuming it's still the stock manifold. The more an engine can breathe, the better.

Dual 250's on a dual quad, open plenum intake manifold would significantly open up the airflow, and be a big departure from the norm. Just add linkage... Edelbrock 7505 - Edelbrock Performer RPM Dual-Quad Air-Gap Intake Manifolds - Overview - SummitRacing.com. Tuning would be fun with those 2 mixers, but not impossible. An open plenum intake would allow adjustments to be less than perfect and still run great.

Tuning is usually accomplished with an CO/O2 sensor in the exhaust pipe, and a diagnostic computer. However, I know guys who will do it just by SMELLING the exhaust. There is not much to adjust, just Idle mixture and Power mixture. It's better to run a little lean than rich... running rich will shorten the life of the exhaust valves. If you're going for REAL performance... take the truck to the 1/4 mile track. Start lean, then keep adding a 1/4 turn each time until you start getting slower again.

In the end, an Impco 425 or OHG 450 would be simple, powerful and reliable. Any chance you could source one instead of messing with 2?

 

ok , my mistake the 250 is on the shelf next to were I was looking .yes they are 2X425ipco mixers on the duel unit .and yes it is a single 425 running the bronco now. to many bit's and pices laying around ...sorry for not gettng my numbers straight first,for street and some off road will the single mixer be good enough?? is the duel mixer going to be a struggle to setup?..I tried to download pix's but it won't work for me..sorry the pix's would help you understand whatI'm trying to do...and it's on an old single plane aluminum intake..

 

Makes sense. The dual mixer setup shouldn't be all that hard to setup, assuming the linkages are synchronized.

Idle should be set when the engine is warm, and the screws should be turned equal turns out from the seated position. The same should be done with the power mixture screw.

How much to adjust it depends on how you are tuning, either with a computer, or on the drag strip. Like I suggested before, If you take your truck to the track with dual mixers, instead of 1... add only 1/8 of a turn on the mixers until you start getting slower.
It may make for a longer day, but power always equals sacrafice.

LPG will never get to the level of energy output as gasoline, but there are other ways to increase the effecieny of it's burn. Since it's high octane, engine compression can reach 15 or 16:1, but thats only for high grade propane. Or you could boost it, which I plan to do sometime in the future.

The cam, intake and headers are a good start. However, too much overlap with the cam can cause issues, because the mixer uses vacuum as the refernce for fuel delivery. Real "Lopey" cams will cause vacuum fluctuations as lower RPMs, making your truck a pain to drive on the street. Franz Hofmann, a long time propane engine builder, reccomends an RV style cam installed straight up, 0 degrees.

Other improvements include building the shortblock for higher compression. Or on the cheaper side, have your cylinder heads shaved .030".

 

well I got into my propain system ..it had started to missfire on acceleration after changing the air filter..and checking plugs ..one plug is pink...they are all bosh plugs and look good but changed them anyhow..what would cause a plug to turn pink?? just the insulator at the electrode..the wires are sprial wound arora..supposed too be good..and the truck has what I belive to be a vacume delay in the advance line..should that be removed on propane??I can't go to a drag strip..we don't have a real one on the island..so tuning that way is out..

 

Is it a misfire on only 1 cylinder, or more? Never heard of a pink plug before, but I suspect you found your problem cylinder. I'll hazard a guess and say it's due to the incomplete burn of the propane. How did you set your mixture?

Check the usuals for the misfire, wires, cap, change the plug. Chuck out the vacuum delay, it's not needed. If it persists, then try richening the mixture a little.

 

well the plug change and air filter change have helped checking the vacuum advance timeing and wondering should the timeing be all in at 2500 rpm ??I played with the mix to the best idle listening for the change of speed and even idle..I don't have a exhaust meter yet..it smell's fine no weird smells ..

 

Suggested by Franz H.... His words, not mine.


For starters, set initial timing 5 degrees more advanced than with gasoline. Recurve the total timing to about 35 deg BTDC at 3000 rpm.

To set the idle, use a gas analyzer and adjust for approx 1% CO. For the larger screw, its best to usually leave it alone unless you have access to a chassis dyno and gas analyzer, then set for 1% at full throttle load.

 

well I played with the timeing checked all the settings befor I started.and found the one advance spring was broken..replaced it with an accell set makes a big differance it is set at 17 btdc and all in at between 2800 and 3000.. now no fart's no wierd shudder slowing down..I seem to have forgotten to check the simple stuff before looking for help thanks guy's ..I do appeciate your help

 

Poor drivability of a propane engine almost always has to do with ignition problems. Propane has a higher ionization energy than gasoline and therefore places higher demands on the ignition system. Mag Wires are often specified for LPG & CNG service (see Understanding Spark Plug Wires).

Propane also has burns at a different rate than gasoline so the advance curve should be optimized for it. Because propane has a higher octane rating than gasoline, a greater amount of initial advance may be used. It also burns at a different rate so less total advance is often required. A general rule of thumb for advance is 14+14+14. That is, 14° initial, 28° total, and 14° of vacuum advance.

Basically, the mechanical advance is set to produce the maximum amount of power and more is not necessarily better. Once mechanical is determined, vacuum advance is set to produce the best fuel economy, and more is not necessarily better.

 

Great advice.

I haven't heard of using the Mag wires before, certainly an upgrade in the future.