xemeanmachine

Hey all, got another one for ya

This ones really got me stuffed. I got a recond 600 vac sec holley for the 351. Haven't changed anything else on the motor. The XE is now back to bagging tires off the line if need be which i'm happy about. It still has a slight flatspot on light acceleration which i'm sure is just an accel pump adjustment.

The primary jets i've changed to 63's, they were 66's.

Now, under load the motor is fine, pulls like all hell... but when cruizing at say 60km/h you can notice a bit of a uneveness... kinda feels like someone tapping the break pedal. Its very random, like theres no pattern to when it happens. If you open the throttle a little bit and start accelerating, the problem is less to no more. If you drive at 60km/h and leave it in 2nd, its even more noticable to the point you can here the motor surging then starving kinda thing.

Any suggestions??

Pete

STROKEXD

Suggest you take off the metering block and blow the jets and orifices out with compressed air, sounds like a partially blockage somewhere. Also do the 4 air-bleeds on top of the carb.

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TruBlu351

It sounds similar to what is termed surging. ie: not missing, but as you described, slight cycles of accleration and deceleration.

If this is the case, it is normally caused by a lean situation in the carb. It's not a jet issue as the main circuit is hardly working at cruise.

Just wind your idle mixture screws out 1/4 to 1/2 turn each and go for a drive.

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XE Falcon
393 Tremec TKO 9"

9psi EB

The surging could also be a distributor or timing chain problem, unrelated to the carby?

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xemeanmachine

Hey TruBlu351, when i had a vacume guage on the motor, I adjusted the idle mix until I got the highest reading. Should I still be taking it a bit further like you suggest?

TruBlu351

The vacuum gauge method works well for tuning. Get it just right and then fatten the mixture a little and see how it goes.

Just wind them out from where they're at now. If it works great, if it doesn't you may have to persue another avenue.

Some cars, depending on cam/heads/combo etc, just need a personal tune/tweek to make them work the best.

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XE Falcon
393 Tremec TKO 9"

xdclevo

It is good to have a strong vac, but i go on what the motor likes. I like the best combination of idle in park and also in drive.
When i have a nice "non stinky exhaust", good idle in park and drive together and no bogging or hesitation, i am happy.(I think i am here finally)
The best advise above is do a small change, then go for a drive. You will then see how the changes affect all of your driving.

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10.70 @ 125.00 on the black fun top
408 Cube Cleveland.

9psi EB

Another quick thought also, it may help, or it may not,
Grab a can of WD-40 or similar (even carby cleaner will do) and spray along where the head / intake manifold join, while it's idling.
If it seems to idle better when spraying, this will indicate a leaky intake manifold gasket, which will play tricks with idle mixtures, and contribute to surging also.

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xemeanmachine

Thanks guys

9psi, i've already done those checks, theres no leaks there and she idle's fine. The problem is only when cruizing. I'll have a play with it on the weekend and richen it up a tad and see what happens.

Is there any way all of the outputs on the dizzy going to the plugs can ark?

xemeanmachine

Ok, i've richened it up by 1/2 a turn each side, and it seamed to idle a little better. Took it for a drive and the surging is still there. got it home and took it another 1/4 of a turn and it started to idle worse again. Its got me stuffed haha