Reply
 
Thread Tools Display Modes
 
Old 09-19-2016, 05:02 PM   #11
Mini-Skoolie
 
Join Date: Sep 2016
Posts: 16
Quote:
Originally Posted by cadillackid View Post
did you adjust the floats in the new carb when you put it on? trying to think of all the gotchas.. is it hitton on all 8 cylinders? if its idling does the engine shake? or if you go back to the exhaust and put your hand near the outlet is it smooth or a lot of rhythmic pulsing? trying to figure out if we just have a good old fashioned "miss" only hitting on 6 or 7 cylinders..

-Christopher
It idles smooth as can be, I have not adjusted the floats since the installation. I don't think I explained this correctly before so let me try to recap. You'll run fine, there is a bit of a power loss (compared to those first 200-300mi like I said) but it isn't significant when you're running on flat ground (hills can drop me to 25mph depending on the grade and the speed/RPM at which I started at and I don't mean 10% grades I'm talking sometimes a 5% grade will bring me grinding down to second gear (it may also be helpful to note this is a 4speed automatic [old Allison I believe])).

Okay so the minor power loss aside the real symptom of concern is that I can drive for a few hours (or sometimes less) and then out of nowhere it is like the engine starts to feel almost like its cutting off, it quiets down, the power loss is huge and before you know it you've dropped from 55 down to 40 and hitting the accelerator down to the floor does nothing you continue to slow until you hit 40, and then it just feels weak as hell and you can't accelerate back up. It did this before the timing adjustment and at this point you can usually cruise at 40 till it does it again and you slow more. Before the timing adjustment this is when the backfiring (detonating in the exhaust like you mentioned, no true backfires where you're getting that monumental gun shot sound of exhaust valves being open during combustion). Now at this point the bus is just slow, and I'd pull over usually get some fuel, food whatever. Hop back in the bus after as little as 15 minutes and you can get back up to 55 no problem for a few more hours.

Which leads me more in the direction of some spark/distributor related problem unless there is some electronic system I'm not aware of that could be bugging out.
snorris8236 is offline   Reply With Quote
Old 09-19-2016, 05:06 PM   #12
Mini-Skoolie
 
Join Date: Sep 2016
Posts: 16
Quote:
Originally Posted by cadillackid View Post
did you adjust the floats in the new carb when you put it on? trying to think of all the gotchas.. is it hitton on all 8 cylinders? if its idling does the engine shake? or if you go back to the exhaust and put your hand near the outlet is it smooth or a lot of rhythmic pulsing? trying to figure out if we just have a good old fashioned "miss" only hitting on 6 or 7 cylinders..

-Christopher
So my rambling aside, thank you again. Now my questions for you would be, how can I thoroughly check I'm hitting all 8, just check the spark at each cylinder and recheck each plug to make sure they didn't get fouled up (I've put ~1000 mi since I replaced them). Also when I get that major power loss it doesn't feel smooth it sometimes kind of bucks (essentially: power loss... lets go... wait no power loss... wait lets go... okay now f*** it I quit)
snorris8236 is offline   Reply With Quote
Old 09-19-2016, 05:36 PM   #13
Bus Nut
 
Carytowncat's Avatar
 
Join Date: May 2016
Location: Richmond Virginia
Posts: 805
Year: 1984
Engine: 366 Big block Chevy! :) w/ Stick shift
That feels electrical/ spark to me; on/ off is often a symotom of electrical.

Plugs can foul up if a valve seal is bad which is super common on the 80s gmcs.
Also distributor or cap and rotor? I just had a flash of the coil. That is a part that would heat up and lose connection, and act intermittent if it id going bad.

Plus those coils have quite a few connections in the dis cap that could be coming in and out. My vision suggests the coil.

Btw this is the guy who visited
Carytowncat is offline   Reply With Quote
Old 09-19-2016, 06:11 PM   #14
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 3,418
Year: 1991
Coachwork: Carpenter
Chassis: International S3800
Engine: DT360
Rated Cap: 7 Row Handicap
if it has HEI distributor it sure sounds almost like that module is missing spark..

im assuming when its running real bad that you pull over it still idles smooth?..

your trans is likely the AT545? (makes a whistle / whine when shifting first to second)..

if its firing off backfires into the exhaust pipe.. (not under the hood but under the bus).. then it definitely sounds like ignition.. I suppose you could have a valve sticking open but from your descriptions it doesnt sound like that..

fouled plugs would be fouled even after the bus sat stopped.. esp if they were oil fouled... fuel fouled they may dry up but that would still indicate that spark had failed going to the cylinder...

I had a rare case on one of my hotrods where the hotter my engine got the lower my fuel pressure went unti it couldnt fill the carb up... id sit, cool down and then go again.. my issue was fuel lines were too close to the exhaust and were getting hot.. causing the fue to vaporize in the lines before the carb.. the gauge is what caught that one... id start out with a nice 6-9 PSI and after driving awhile when i stopped the gauge would be reading close to 0 and id have power loss.. I popped out the carb under the hood a bit sometimes when that conditon existed as i was leaning out.. but did not pop in the exhaust under the car...

that car also ran better and longer on a cool morning and longer the first time you started out than after it sat.. .so for instance I might drive on a cool morning for 100+ miles when I first started.. but park and then in the afternoon Id only drive 40 or 50 before id sputter... and then look to see my clear fuel filter mostly empty and the gauge on zero... never had anything like that before or after that one car..

I fixed that by replacing my metal lines with AN rubberized steel and moving them away from the engine as much as possible.. and then I ran my fan more aggressively to keep the engine compartment temps down...

-Christopher
cadillackid is offline   Reply With Quote
Old 09-21-2016, 01:56 PM   #15
Bus Crazy
 
Stu & Filo. T's Avatar
 
Join Date: Sep 2013
Location: Vacaville, Ca
Posts: 1,198
Year: 1988
Coachwork: Crown / Pusher
Engine: 8.3 Cummins
Buddy of mine used to have a 240Z that would lose power & die but would restart after a couple minutes, what he found was there was a tiny piece of rust flake in the tank that would get pulled oner the fuel pick up, dropped the tank had it boiled out no more problems.
Stu & Filo. T is offline   Reply With Quote
Old 09-21-2016, 02:47 PM   #16
Mini-Skoolie
 
Join Date: Sep 2016
Posts: 16
Quote:
Originally Posted by Carytowncat View Post
That feels electrical/ spark to me; on/ off is often a symotom of electrical.

Plugs can foul up if a valve seal is bad which is super common on the 80s gmcs.
Also distributor or cap and rotor? I just had a flash of the coil. That is a part that would heat up and lose connection, and act intermittent if it id going bad.

Plus those coils have quite a few connections in the dis cap that could be coming in and out. My vision suggests the coil.

Btw this is the guy who visited
Hey man! Good to bump into you on here, let me know when you want some company we definitely want to see your bus.

I think replacing the distributor may not hurt and isn't terribly bank breaking either.
snorris8236 is offline   Reply With Quote
Old 09-21-2016, 03:06 PM   #17
Mini-Skoolie
 
Join Date: Sep 2016
Posts: 16
Quote:
Originally Posted by cadillackid View Post
if it has HEI distributor it sure sounds almost like that module is missing spark..

im assuming when its running real bad that you pull over it still idles smooth?..

your trans is likely the AT545? (makes a whistle / whine when shifting first to second)..

if its firing off backfires into the exhaust pipe.. (not under the hood but under the bus).. then it definitely sounds like ignition.. I suppose you could have a valve sticking open but from your descriptions it doesnt sound like that..

fouled plugs would be fouled even after the bus sat stopped.. esp if they were oil fouled... fuel fouled they may dry up but that would still indicate that spark had failed going to the cylinder...

I had a rare case on one of my hotrods where the hotter my engine got the lower my fuel pressure went unti it couldnt fill the carb up... id sit, cool down and then go again.. my issue was fuel lines were too close to the exhaust and were getting hot.. causing the fue to vaporize in the lines before the carb.. the gauge is what caught that one... id start out with a nice 6-9 PSI and after driving awhile when i stopped the gauge would be reading close to 0 and id have power loss.. I popped out the carb under the hood a bit sometimes when that conditon existed as i was leaning out.. but did not pop in the exhaust under the car...

that car also ran better and longer on a cool morning and longer the first time you started out than after it sat.. .so for instance I might drive on a cool morning for 100+ miles when I first started.. but park and then in the afternoon Id only drive 40 or 50 before id sputter... and then look to see my clear fuel filter mostly empty and the gauge on zero... never had anything like that before or after that one car..

I fixed that by replacing my metal lines with AN rubberized steel and moving them away from the engine as much as possible.. and then I ran my fan more aggressively to keep the engine compartment temps down...

-Christopher
Yeah it runs smooth when I pull over and just let it idle.

The previous owner put a really cheap universal electric fuel pump on it, well really two (one feeds the generator if you have it running), the generator one I noticed was leaking so I removed it and stuck just a piece of fuel line there to prevent leaks (that was all after this problem was noted though). So I'm debating on just replacing both fuel pumps. I did a little googling this morning and it seems the fuel pressure should be around 7-9psi at idle and no less than 4 at full throttle. The pump on there is this:
https://www.amazon.com/Mr-Gasket-12S...rb_top?ie=UTF8

It gives a range of 4-7psi and is of unknown age so maybe it has been sucking up crap and is struggling to perform over long periods of time?
snorris8236 is offline   Reply With Quote
Old 09-21-2016, 03:08 PM   #18
Mini-Skoolie
 
Join Date: Sep 2016
Posts: 16
Quote:
Originally Posted by Stu & Filo. T View Post
Buddy of mine used to have a 240Z that would lose power & die but would restart after a couple minutes, what he found was there was a tiny piece of rust flake in the tank that would get pulled oner the fuel pick up, dropped the tank had it boiled out no more problems.
Man I hate the idea of dropping the tank but after rethinking all these options this is a real possibility since both fuel pumps are technically gravity feed (sitting on the side of the tank) it could easily be something silly like this. Well I'll start with this and work my way through fuel pump and spark issues next and see if I can get this figured out. Will update when I have some news.
snorris8236 is offline   Reply With Quote
Old 09-21-2016, 04:29 PM   #19
Bus Nut
 
Join Date: May 2016
Location: Georgia
Posts: 462
Year: 1987
Coachwork: Carpenter
Chassis: IH
Engine: IH 9 Liter
Rated Cap: 66 + driver
Hang on ... I wonder ... ... ...

Your fuel tank isn't building up a vacuum, is it? Next time it gets weak, crack open the fuel cap. A gush of air going into the tank is a fair indication this could be the problem. After venting the tank, see if power is back to normal.
Brad_SwiftFur is offline   Reply With Quote
Old 09-21-2016, 06:02 PM   #20
Bus Geek
 
Join Date: May 2009
Location: Columbus Ohio
Posts: 3,418
Year: 1991
Coachwork: Carpenter
Chassis: International S3800
Engine: DT360
Rated Cap: 7 Row Handicap
Quote:
Originally Posted by Brad_SwiftFur View Post
Hang on ... I wonder ... ... ...

Your fuel tank isn't building up a vacuum, is it? Next time it gets weak, crack open the fuel cap. A gush of air going into the tank is a fair indication this could be the problem. After venting the tank, see if power is back to normal.

great idea I hadnt thought of!!.. and one i had bite me once in a car where the fuel tank vent was plugged

-Christopher
cadillackid is offline   Reply With Quote
Reply

Tags
carburetor, chevy

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


» Virginia Campgrounds

Reviews provided by

Powered by vBadvanced CMPS v3.2.3

All times are GMT -5. The time now is 01:02 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.