ForumsBasic TrainingOnline Maintenance ManualsThe M715 Zone Vin RegistryVPW's M715 Parts ListGalleriesLinks

Go Back   M715 Zone > General Tech > Open Discussion

Open Discussion Open Discussion for all M715 series trucks

Reply
 
Thread Tools Display Modes
  #1  
Old June 24th, 2020, 06:25 AM
farmer farmer is offline
Private
 
Join Date: May 2016
Location: Central NH
Posts: 70
farmer is a Soldier
Default Lack of power in 4th

Been battling issues with my truck, and have been down many rabbit holes. The upside is I have learned a ton and fixed a ton of stuff, but I'm still struggling to maintain 30 MPH in 4th gear with the original 230.

Led me to find a takeout engine locally, priced right. I looked it over and the guy says he's done messing with it, hes just putting a diesel in. I ask what his issue is with the motor and low and behold, it struggles to maintain speed in 4th.

For reference, both engines still have the original Holley carb, and have the civilian distributor swapped in, still running points, 12 volt converted. I haven't investigated as to whether or not he had the vacuum advance hooked up, but I've noticed little difference with or without in my testing. My carb was freshly rebuilt

Has anyone else fought this battle and actually won? I have a pertronix kit coming to eliminate the points, but I guess part of me is questioning the carb, so I bought a NOS carb kit as well. I'm wondering if the power valve in the carb is malfunctioning when the motor is lugging.

I have the stuff to swap the engine for a chevy v8 but I feel that its a disservice to this old truck.
Reply With Quote
  #2  
Old June 24th, 2020, 06:41 AM
Beast's Avatar
Beast Beast is offline
Sergeant

 
Join Date: Feb 2004
Location: Silver Lake Sand Dunes MI
Posts: 1,311
Beast is a Soldier
Default

What is the compression of each cylinder? If they are good then look for issues like timing due to lack of vacuum advance, or fuel starvation (blocked fuel line, miss-adjusted carb) or an air restriction (blocked or dirty air filter). Also check to make sure the throttle cable is not kinked and is opening the carb fully. I had this issue once and it acted like the truck was down on top end power. Once I found the bad cable and replaced it, the truck ran like normal.
__________________
Dave
Delta Team Decals: http://www.deltateamdecals.com/
Reply With Quote
  #3  
Old June 24th, 2020, 07:03 AM
farmer farmer is offline
Private
 
Join Date: May 2016
Location: Central NH
Posts: 70
farmer is a Soldier
Default

Quote:
Originally Posted by Beast View Post
What is the compression of each cylinder? If they are good then look for issues like timing due to lack of vacuum advance, or fuel starvation (blocked fuel line, miss-adjusted carb) or an air restriction (blocked or dirty air filter). Also check to make sure the throttle cable is not kinked and is opening the carb fully. I had this issue once and it acted like the truck was down on top end power. Once I found the bad cable and replaced it, the truck ran like normal.
Thanks for the quick reply.

Front 5 cylinders has decent compression~120-130, cyl 6 is ~90.

I've messed with the timing a ton, although I haven't verified the mechanical advance is functioning properly, I'll add that to my list. The original igniter didn't have a vacuum advance, I figured the distributor would be fine with it no hooked up.

I have some fuel line concerns from a crummy tank, I ought to toss my boat tank in and try to see if that eliminates the issue.

Throttle cable kinking is new to me, I's definitely have to check that out.
Reply With Quote
  #4  
Old June 25th, 2020, 08:18 PM
brute4c's Avatar
brute4c brute4c is offline
Grand Poobah
 
Join Date: Sep 1998
Location: North Central Wisconsin
Posts: 11,631
brute4c is a Soldier
Default

There was a member with the same problem many years ago...what he found eventually was that the leaf spring like tensioner arm on the points set was in the wrong place and wasnt providing the correct tension on the points...basically it was on tghe wrong side of the mounting bracket and that was enough to keep the pressure down enough that as the load got higher, the points werent keeping up.

In the following image, it is the flat metal plate that runs from the points past the arrow of #3 to the mount bolt that is in the line to the #4 arrow....hopefully that is clear...
__________________
Lord send your Holy Ghost into our hearts and make the desire of our hearts Your Will.

Pro-choice, that's a LIE, babies don't choose to die!!
Reply With Quote
  #5  
Old June 26th, 2020, 05:28 AM
Nailhead's Avatar
Nailhead Nailhead is offline
Corporal
 
Join Date: Aug 2015
Location: Longmont, CO
Posts: 953
Nailhead is a Soldier
Default

Quote:
Originally Posted by brute4c View Post
There was a member with the same problem many years ago...what he found eventually was that the leaf spring like tensioner arm on the points set was in the wrong place and wasnt providing the correct tension on the points...basically it was on tghe wrong side of the mounting bracket and that was enough to keep the pressure down enough that as the load got higher, the points werent keeping up.

In the following image, it is the flat metal plate that runs from the points past the arrow of #3 to the mount bolt that is in the line to the #4 arrow....hopefully that is clear...
Not to contest an apparent success, Jon, but wouldn't that problem manifest itself at the same RPM in any gear? After all, it's the engine that's being made to work under a load, not the point spring (as I understand it).
Reply With Quote
  #6  
Old June 26th, 2020, 08:22 AM
farmer farmer is offline
Private
 
Join Date: May 2016
Location: Central NH
Posts: 70
farmer is a Soldier
Default

Quote:
Originally Posted by brute4c View Post
There was a member with the same problem many years ago...what he found eventually was that the leaf spring like tensioner arm on the points set was in the wrong place and wasnt providing the correct tension on the points...basically it was on tghe wrong side of the mounting bracket and that was enough to keep the pressure down enough that as the load got higher, the points werent keeping up.

In the following image, it is the flat metal plate that runs from the points past the arrow of #3 to the mount bolt that is in the line to the #4 arrow....hopefully that is clear...
Interesting. Thats the kind of experience I love about forums, thank you.

I've been into the ignition and rebuilt it all, so the probability of the spring being setup incorrectly is pretty high. I'll know for sure when I get the Pertronix points eliminator in.

Nailhead: my thinking is that the spring not applying enough tension would contribute to a weak spark, which the engine would run ok with no load, add significant load and the engine wont run as well on the weak spark. Add higher RPM and I'd bet the spring would "float" like valve springs if there was inadequate tension.

Parts should be in today, I'll let you know how it goes.
Reply With Quote
  #7  
Old June 26th, 2020, 01:52 PM
kwai's Avatar
kwai kwai is offline
Sergeant

 
Join Date: Dec 2006
Location: Houston, Tx
Posts: 3,138
kwai is a Soldier
Default

The ignitor also has a mechanical advance using springs and centrifugal weights. There is no vacuum advance. if the mechanical advance is frozen or sticky that would also cause a problem as the throttle is opened.
Reply With Quote
  #8  
Old June 27th, 2020, 08:10 AM
Scott in Ct Scott in Ct is offline
Civilian
 
Join Date: Nov 2011
Location: Connecticut
Posts: 9
Scott in Ct is a Soldier
Default

On top of the page is the Basic training section. There under faq is some good info that may help with your trucks problem. Good reading at the very least. Good luck . Scott
Reply With Quote
Reply

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

Forum Jump


All times are GMT -7. The time now is 02:04 AM.

 

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
1998 - 2020


This site is owned and operated by:
M715 Zone, LLC
President: Jon Schmidt, User ID=brute4c
If you have any suggestions, comments, problems or questions, contact:  brute4c@m715zone.com

Use of this site means you understand and agree to our TERMS OF USE

Copyright Notice:
This web site is subject to the protection of the copyright laws of the United States and other countries. Except for Personal Use Only, you may not modify, copy, distribute, transmit, display, perform, reproduce, publish, license, create derivative works from, transfer, or sell any information obtained from any part of the M715 Zone website without the prior written permission of M715 Zone, LLC.

Written permission can only be obtained by contacting
brute4c@m715zone.com

Copyright 1998-2020