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I recently went thru my entire fuel system on my M37. relined gas tank, brand new drop in stainless steel filter in the tank, all brand new armoured lines up to the NOS fuel pump and NOS carb. you cant do much better that that!

anyway, as this truck is at a remote location, and I dont get to it often, its weeks between when I can run it.

Last time I was there, I was making adjustments to timing, etc...I noticed the carb was running poorly.

WT?

I took it for a ride, and coming to a stop, the truck just died.. would not idle.. fast idle, its fine...under load, acceleration, just fine.

I tried adjusting it.. the idle mix screw, completly out or completly in, did little to nothing...

I got to thinking, using past memory, having this issue before, ended up that the carb had sediment, or crap in it. requiring a cleaning

now how could this be? its all new.. I did run the old carb for a spell on the truck after the lines were put in, just for the reason that IF I left a small spec of something in the lines, it would flush out before I put my nice brand new expensive carb on!

anyway.. the entrie system.. its all new. I bought a NOS fuel pump and NOS carb from VPW.. at the time of purchase, I voiced my concern over the NOS units over a more modern rebuilt unit as I read about the interanl diaframs and such may or may not be compatiplabe with todays fuels.

they said that the NOS carb, even though built in the 80's are fine with todays fuels, and that I should NOT be seeing any gasket failures due to the fuels.. they think, however, that the gaskets could shrink, and cause vacuum leaks.. and that my first thing to do should be to tighen all screws around the carb and see it that fixes it.

I will try that first.. but...I think I may pull it apart as well and clean out what offices I can with a can of carb cleaner.

anyone have any similiar experiences? anyone have a general guildline for me to start?

Have anyone one of you had faulures with the NOS units, maybe internal parts "crumbling" and leaving fine particales to make its way to the carb jets or other orifices?

thanks!

If my memory serves me right........more than a few folks have had problems with NOS fuel pumps on here. Don't know about carbs because NOS carbs are far and few between. It does sound like a vacuum leak or float level set wrong. If you haven't ruled out the NOS pump as the problem........you can re-install the old carb and see how she runs. If it idles fine.......it's the NOS carb. If not......it's the NOS pump. Good luck.

regards,
bob

If the idle screw does nothing, it might be running off the high speed circuit. What is the idle speed set to? I think it should be around 500 rpm. You really have to start at zero with the adjustments.

thanks for the replies.

well, had an hour or two to fiddle with the truck on Sunday before getting back on the road for home.

Started at the carb..

took it off the truck, and opened it up for the first time it was assembled at the factory.

yep.. as expected. full of sediment.. not fine rusty stuff as I had seen in the past, coming from rusty tank and fuel lines, but more of a yellowish in color fine silt of sorts. not attached to the walls, like in years of build up or anything like that.. just floating around in the bowl, loose enough to come out by dumping it

not sure what this is.. is the inner diaframn on a fuel pump this color?

anyway, I did clean the carb thoroughly and put back on the truck.

I didnt fire it up, because I didnt want the same thing to happen. (i.e. fill with the same sediment)

It will need to wait until I return with a modified fuel line from the fuel pump to the carb, containing a clear in line filter, so I can see if more of the sediment comes from the fuel pump or further down the line.

my guess is the fuel pump is the culprit, seeing as I have a 100% cleaned tank, in tank stainless filter, and brand new fuel lines from the tank to the pump.

I already talked to Steve at Vintage about this, and as expected, he will honor any return on it, if its either carb or the pump. he did offer some assistance on the trouble spot to look for, like tightening the carb screws (they were tight) as well as other palces to look.

will see once I get her running again with an additional fuel filter just before the carb.

Doesn't sound NOS to me, at least the new part. That sediment is what I would expect to find in an old carb that has had a bunch of fuel run through it. Particles small enough to get through the filter settle out and some fuel evaporates, leaving the sediment behind. That's the condition of most all old used carbs I've worked on.

Doesn't sound NOS to me, at least the new part. That sediment is what I would expect to find in an old carb that has had a bunch of fuel run through it. Particles small enough to get through the filter settle out and some fuel evaporates, leaving the sediment behind. That's the condition of most all old used carbs I've worked on.

thanks for your thoughts on this.


well, what if the Fuel Pump diaframn is disintegrating? its the last mechanical thing JUST before the carb.. wouldnt deteriorating fuel pump innards find them selves very fast in a carb bowl?

thats what I am thinking, anyway.

Ill try the clear filter JUST before the fuel enters the carb bowl and see if I catch any more debris..

now, all that said, I noticed that the inside of the carb WAS pretty messed up. as they are zinc (or aluminum?) in construction, perhaps the inside of the bowl plating has "flaked" off and that is what I seen in there? It could have been the yellowish tinted stuff I drained out: PLATING

If indeed your fuel pump is NOS, diaphragm deterioration is a sure issue. Couple that with today's ethanol gas, and you have double trouble. What I'm saying is simply this, FACT, anyone who even sells a NOS pump without first going into it to replace the diaphragm with the latest current production component CERTAINLY does not have your best interest in mind. Even the best material doesn't like ethanol gas blends, so a NOS unit with a 40-50 year old diaphragm doesn't stand a chance. Best to purchase only ethanol free gasoline if you have a source in your area.

Have you thought about the HUGE chance you are taking in regards to complete engine destruction? If the diaphragm cracks allowing gas to dump directly into the oil pan; even the best oils will become diluted to the point of being useless in a VERY SHORT amount of run time. Sediment in the filter is the LEAST of your worries; the BEST advice anyone can offer you is to get that NOS pump off your engine ASAP. Get the core pump rebuilt with current production internals before returning it to service. An even better suggestion is to replace the mechanical pump with a quality in-line electric pump, which will eliminate all possibility of gas being dumped directly into your oil pan.