Brought to you in part by:

.

Shop Eastwood for your Auto Restoration Needs!


  Mustangsandmore Forums
  Ford Racing
  secondary bog

Post New Topic  Post A Reply
profile | register | preferences | faq | search

UBBFriend: Email This Page to Someone! next newest topic | next oldest topic
Author Topic:   secondary bog
68bbstang
Journeyman

Posts: 26
From:
Registered: Sep 2001

posted 07-17-2002 12:25 PM     Click Here to See the Profile for 68bbstang   Click Here to Email 68bbstang     Edit/Delete Message   Reply w/Quote
First off, this may not be the normal place to post this problem, but I'd like to get a consensus from the brain trust. I have a .040 over 460 in my jetboat. It is basically stock (8.5:1) with a Holley 4160 that has been converted with a secondary metering block, Weiand stealth and log exhaust. The jets are 72 primary and 82 secondary and plug color is good.
After replacing the secondary diaphragm (old one was bad), when I launch, the primaries pull well and when the secondaries come in there is a bog, or flat spot. I have a yellow spring in it. Even at speed, when I get into the secondaries it kind of noses over. I realize this is a different scenario that 1/4 mile, but my thought is that my pump is a huge dyno and the principle is the same.
I suspect I need to fatten the secondaries, but you have to be careful doing jet changes on a boat. I have an adjust-a-jet in the '68 and it works well, so I may get another for the secondaries on the boat.
Sorry for the long post.

IP: Logged

steve'66
Gearhead

Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000

posted 07-17-2002 09:59 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
My thought is that the yellow spring is way too light for a 460. Try the brown one and see how it works.
I agree that a jet is a big water pump, it'll rev as high as the h.p. allows instantly and the boat speed will take its time to catch up. But your secondaries are coming in too soon with the yellow spring, like a dp'r w/o the secondary accel. pump to help it not bog.

SteveW

IP: Logged

mustangboy
Gearhead

Posts: 652
From: Ont, Canada
Registered: Mar 2002

posted 07-17-2002 10:11 PM     Click Here to See the Profile for mustangboy     Edit/Delete Message   Reply w/Quote
The nice thing about tuning a boat is you can see when the secondaries are opening so you know exactly whats happening.I agree with Steve it sounds like they are opening too soon,especially if the motor recovers after a few seconds and starts to pull hard again.

IP: Logged

68bbstang
Journeyman

Posts: 26
From:
Registered: Sep 2001

posted 07-17-2002 10:44 PM     Click Here to See the Profile for 68bbstang   Click Here to Email 68bbstang     Edit/Delete Message   Reply w/Quote
I'll try the heavier spring, but the odd thing is, it doesn't really recover. It continues to accelerate to a minor degree, but I should get more RPM and pull out of it when they open. I can hear when they close and there is very little, if any decel running on the primaries. I just can't figure out why it noses over.

IP: Logged

steve'66
Gearhead

Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000

posted 07-17-2002 11:11 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Lets pump that jet up!

It'd be a shame to let a 455 olds blow by you.

SteveW

IP: Logged

bluestreek
Gearhead

Posts: 1289
From: Athens,GA
Registered: Jul 2001

posted 07-18-2002 10:28 AM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
You could try cracking just the secondaries open by hand and see how the engine reacts. If it bogs or dies instantly, then this could indicate a lean condition from a stopped up secondary metering system or low initial timing. If it just runs rough and shaky, then it could be rich. It's hard to believe that 82 jets in a 4160 could be too small.

Dan

IP: Logged

Just Strokin
Gearhead

Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001

posted 07-18-2002 03:13 PM     Click Here to See the Profile for Just Strokin   Click Here to Email Just Strokin     Edit/Delete Message   Reply w/Quote
By chance, did you leave the check ball out when you replaced the diaphram?

IP: Logged

Moneymaker
Administrator

Posts: 19704
From: Lyons, IL, USA
Registered: May 99

posted 07-18-2002 03:31 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Good question?

------------------
Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator

NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl

IP: Logged

68bbstang
Journeyman

Posts: 26
From:
Registered: Sep 2001

posted 07-19-2002 12:05 PM     Click Here to See the Profile for 68bbstang   Click Here to Email 68bbstang     Edit/Delete Message   Reply w/Quote
I made sure the check ball is in. One thing that came to mind, is to recheck the timing. Since this is a boat, and the timing pointer was repositioned to the motor plate, I don't know how accurate it is. I'll have to check TDC on 1 and mark the dampener and reset the timing. I can't imagine I'll get that much more from the secondaries with more advance. I just remembered...when I took it out the first time after rebuilding the carb, I jumped on it at idle and it sneezed. After I got some temp in the cylinders, it didn't do it.

IP: Logged

bluestreek
Gearhead

Posts: 1289
From: Athens,GA
Registered: Jul 2001

posted 07-19-2002 12:47 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
Don't be afraid to bump up the base timing a little higher than stock specs to cure off idle sluggishness. I usually just bump up the tiiming by ear until the throttle response is crisp and then give it a "crank and drive test". Afterwards I check the advance curve to be sure it's working smoothly and not advancing to far after any adjustments. It's a good idea to have an inline fuel pressure gauge to monitor fuel feed to the carb too if you don't already have one. The "nosing over" that you mentioned can be a sign of fuel starvation caused from a weak pump or stopped up fuel system.
Have a good weekend!


IP: Logged

All times are ET (US)

next newest topic | next oldest topic

Administrative Options: Close Topic | Archive/Move | Delete Topic
Post New Topic  Post A Reply
Hop to:

Contact Us | Mustangsandmore Front Page

Copyright 2003, Steve LaRiviere. All Rights Reserved.


Ultimate Bulletin Board 5.47d

Amazon Honor System Click Here to Pay Learn More

[Build a free Mustangsandmore.ws Home Page!]

[About M&M][Acronyms][Calendar][Chat][Classifieds] [Members' Pics] [M&M Mug Shots]

[ Mustangsandmore.com Bookstore] [Mustangsandmore.com T-Shirts][Tech Articles]