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RoadRoman · 06-08-2016, 02:20 PM

Quote:

Originally Posted by Paul and Tam

Problem #1: Failing to start cold. One more possibility is a failing mechanical fuel pump. Generally a failing accelerator pump in the carburetor will show as a lean stumble when you go from idle to half or more throttle in drive (warm engine), as when accelerating away from a stop light. If you step on the gas and you get a lean stumble instead of acceleration you typically have a bad accelerator pump in the carb.

- Paul

Awesome, I'm having the carb rebuilt, hopefully that will fix the problem. Thanks a lot for the advice!

Grosspoluter · 06-08-2016, 10:22 PM

OK so replaced fuel filters most of the fuel line and installed a electric pump
I haven't gone for a test ride yet because the pump isn't permently wired in yet..
I bought a cheap mr gasket fuel pressure gauge and installed it right after the electric pump (pump is right in front of the fuel tank I believe the gauge was a P.O.S.
It gave a reading of 3psi
Weather the engine was running or not, also the gauge leaked fuel, and when the gas got on the plastic gauge window it fogged the plastic making the gauge almost unreadable
The fuel pump (carter P4070) does pump fuel to the manual pump and it is quiet
I still would like to install a gauge but I'll spend the next day or two permently wiring it in so I have another question...
Should the pump be running all the time or should I install a switch to run it only when I want.
Right not the engine will run with the pump running or not

WayneG · 06-09-2016, 02:52 AM

3 PSI may be a little low, 5 would be better, but a cheap gauge is not a reliable measure.

A electric fuel pump should be hooked up to run only when the engine is running.
To do that it should have a safety interlock that prevents it from pumping unless the ignition switch is on and there is oil pressure.
Too many people leave out the oil pressure switch, which is a bad idea. The reason for it is that if you break a fuel line after the electric pump or your carb float sticks open, it will be pouring fuel some place creating a fire hazard. If the engine is not running because of lack of fuel, there will be no oil pressure and the fuel pump will stop pumping.
I found this diagram for a fuel pump hookup, there may be better methods

Grosspoluter · 06-10-2016, 08:42 AM

With the understanding that the only dumb question is the unasked one....
When I install the fuel pressure guage where should I put the sensor
(this guage will be dash mounted)
Between the electric and mechanical pump or between the carburetor and mechanical punp? And what should I expect to see as far as readings?
Will pressure reading drop at wide open throttle, or under load? Because the pump is now feeding the carburetor?

bkahler · 06-10-2016, 06:40 PM

I guess it would depend on what you're most concerned about, output of the electric pump or the output of the mechanical pump. If I was installing it on my Argosy I would want to know what the pressure is going into the carburetor.

Actually on my Argosy I'm installing a fuel pressure sender just before the carburetor (actually throttle body In my case) because if the fuel pressure is good at that point then any problem I might experience is not fuel feed related.

WayneG · 06-11-2016, 05:11 AM

I went a little over kill on my pressure gauge, but it is worth it. When I installed my TBI kit I was having all kinds of fuel problems, to make a long story short, it turned out I was sucking air in the fuel tank causing the electric pump to loose pressure. The full story
I used a surplus digital sender unit with a analog output to a digital dash gauge:

The strip above has 3 color LED strip, Red for low pressure, Green for OK, Yellow for high pressure. My Throttle body uses 30 PSI inlet pressure.
Your best place to measure fuel pressure is right at the input at the carb because that will tell you if the pumps are working or if the filters are clogged or your sucking air.
Dont forget to install a filter before the electric pump (If you have room) The gas tanks in mine had a lot of rust-dust sloshing in the bottom of the tank so the PO installed a huge filter inline:

Since my latest setup has only one pump in the tank, I have a sock filter on it also to keep it from sucking rust.

Grosspoluter · 06-12-2016, 02:58 AM

As of today I have the electric pump, and a guage up and running
Without the electric pump the pressure at the carb. Was 3-0
With the pump running it's about 4-5!
Guage is installed 6" before the carb.
Just curious how can the pressure read 0 and the engine still run (it ran, idled for about 5 minutes with 0 psi.) at that point is it just engine vacuume pulling in fuel?

bkahler · 06-12-2016, 04:55 AM

Quote:

Originally Posted by Grosspoluter

As of today I have the electric pump, and a guage up and running
Without the electric pump the pressure at the carb. Was 3-0
With the pump running it's about 4-5!
Guage is installed 6" before the carb.
Just curious how can the pressure read 0 and the engine still run (it ran, idled for about 5 minutes with 0 psi.) at that point is it just engine vacuume pulling in fuel?

What were the circumstances where the engine was running and you had 0 psi?

If the electric pump was off and the engine was running then the mechanical pump was having to pull fuel through the electric pump, I can see where that might reduce the pressure to a minimal amount. The electric pump will likely create a little bit of restriction to flow when not running.

Also the gauge itself is likely to not be quite as accurate at the lower and upper ends of it's range. Most instruments provide accurate readings towards the middle of their range and as the readings drop towards the minimum or rise towards the maximum the numbers won't be quite as accurate.

Brad

Grosspoluter · 06-13-2016, 05:05 AM

I got a reading of 3-0 with the electric pump installed and NOT running
Engine was just idling
Pressure would start at 3 and slowly drop to 0 in about 3 minuets
With the electric pump
Running and engine at idle the pressure starts at 5 and slowly drops to 4
I agree gauge might not be 100% accurate but I believe it's close
I still haven't gone for a test drive as I doing other repairs on the Motorhome in my driveway
I expect to get out and actually drive it maybe tue. Or wed. Of this week

bkahler · 06-13-2016, 07:23 PM

Quote:

Originally Posted by Grosspoluter

I got a reading of 3-0 with the electric pump installed and NOT running
Engine was just idling
Pressure would start at 3 and slowly drop to 0 in about 3 minuets
With the electric pump
Running and engine at idle the pressure starts at 5 and slowly drops to 4
I agree gauge might not be 100% accurate but I believe it's close
I still haven't gone for a test drive as I doing other repairs on the Motorhome in my driveway
I expect to get out and actually drive it maybe tue. Or wed. Of this week

The only reason I can think of is the engine idle speed is low enough the at idle the pump produces very little pressure. Probably just enough to keep fuel in the bowl and that's about it.

I assume once you rev the engine the pressure builds back up?

RoadRoman · 06-14-2016, 02:58 AM

The carburetor is now rebuilt. Is there a thread on tuning a quadra jet? What all entails adjusting to ensure it runs fine if it's just been rebuilt? Good YouTube video?

WayneG · 06-14-2016, 03:34 AM

Anyone with reasonable skill can use a kit on a Qjet, but getting the passages clean, making sure the shaft bores are not oversized due to wear and getting the plates to seal are not done in a weekend rebuild.
I still believe that having a GOOD carb shop is the best way to go with a Quadrajet rebuild, they know all the little qwerks and how to fix them.
For the brave, this link has the 4M 4MV & 4MC Quadrajet service manual.
http://www.tocmp.com/manuals/Carbs/R...QJet/index.php

RoadRoman · 06-14-2016, 03:19 PM

Quote:

Originally Posted by WayneG

Anyone with reasonable skill can use a kit on a Qjet, but getting the passages clean, making sure the shaft bores are not oversized due to wear and getting the plates to seal are not done in a weekend rebuild.
I still believe that having a GOOD carb shop is the best way to go with a Quadrajet rebuild, they know all the little qwerks and how to fix them.
For the brave, this link has the 4M 4MV & 4MC Quadrajet service manual.
http://www.tocmp.com/manuals/Carbs/R...QJet/index.php

Thanks, I didn't tackle that feat myself. Left it up to a good carb shop for sure. All I felt confident enough to do was pull the four bolts out and get it there, and putting it back in. I just don't know how to set the jets and idle screws..

jonesy 1 · 07-19-2016, 09:59 PM

You use a vacuum gauge .and a tachometer.

RoadRoman · 07-20-2016, 12:16 AM

I did indeed! I figured out the carb, purring like a kitten. Also, dash gauges were flickering when I turn the headlights on and use blinkers. Regrounded the fuse panel box to the chassis with thick gauge wow and that seems to have fixed it. Just in case anyone else is having a similar problem. Although the left turn signal seems dimmer and weaker than the right, at least the dash gauges aren't going off the wall hah

bpg_austin · 07-26-2016, 06:41 AM

Quote:

Originally Posted by RoadRoman

Although the left turn signal seems dimmer and weaker than the righth

Crawl underneath and chase the wires from the turn signal. I bet they're corroded somewhat giving you a poor connection. My headlights did the same thing. About 20 minutes and some new spliced ends and connectors gave me back my headlight. Time and weather sure take their toll under there.

RoadRoman · 07-26-2016, 01:18 PM

Quote:

Originally Posted by bpg_austin

Crawl underneath and chase the wires from the turn signal. I bet they're corroded somewhat giving you a poor connection. My headlights did the same thing. About 20 minutes and some new spliced ends and connectors gave me back my headlight. Time and weather sure take their toll under there.

Awesome! Thanks will do.

Jenniflow · 08-28-2016, 10:21 AM

We had the same problem with vapor lock - poor acceleration, having to pump the pedal, and sometimes total stalls and waiting for it to cool down so the fuel could phase shift again - and discovered an electrical problem killing the rear fuel pump. There's a thread here about it but I've forgotten where it is. One of the experts here can send you to it.

kidjedi · 07-15-2020, 01:21 PM

Quote:

Originally Posted by overlander63

Removing the tiny filter from the inlet of the carb, and installing a more effective one in-line won't hurt a thing.

I was searching for a part number for the carb filter on my 454 and found the above statement. I just want to verify that it's actually a good idea to remove this filter on the carb intake (currently my Argosy doesn't have that filter in the housing on the carb intake anyway) as long as you have another filter(s) on your fuel line. I will be running a cheap in-line 100 micron fuel filter before the electric pump by the tank, and then another 10 micron fuel filter after the electric pump.

Thanks!

rmkrum · 07-15-2020, 01:40 PM

Quote:

Originally Posted by kidjedi

I was searching for a part number for the carb filter on my 454 and found the above statement. I just want to verify that it's actually a good idea to remove this filter on the carb intake (currently my Argosy doesn't have that filter in the housing on the carb intake anyway) as long as you have another filter(s) on your fuel line. I will be running a cheap in-line 100 micron fuel filter before the electric pump by the tank, and then another 10 micron fuel filter after the electric pump.

Thanks!

Not an identical situation, but I had a carburetor inlet fuel filter clog up on a big GM V-8 in my long wheelbase van conversion. It got bad fuel starvation issues.

I added an in-line fine filter, found the bad one, and threw it as far as I could. It was a bear to troubleshoot and the proper replacement part was pure unobtanium.

Was a sintered bronze slug-type filter well hidden in the carb fuel inlet. Too small to handle a single tank of probably dirty gas on a camping trip. The aftermarket filter had much better flow and dirt capacity.

We also won’t talk about the cheap nylon governor gear in the otherwise bulletproof transmission that wire out and tossed the tranny straight into low gear at 65 miles per hour. Talk about rapid deceleration!

Thought the tranny had blown and the first thing I did was look in the mirror for an oil slick and parts trail behind us.

Crawled on the shoulder at 10 mph for several miles. Found an honest dealer tech on a Saturday afternoon that fixed it, replaced the fluid and filter, and showed me how to check it on the road for less than $100 bucks. He also gave me a spare gear. Added a tranny cooler and never had another issue.