|
Author
|
Topic: secondary bog
|
68bbstang
Journeyman Posts: 26
From:
Registered: Sep 2001
|
posted 07-17-2002 12:25 PM
   
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
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
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
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
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
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
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
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
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
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 |
Mustangsandmore Forums
UBBFriend: Email This Page to Someone! 
