The V8 Owners Forum -

Hi Guys
After taking the car out a few times now I am finding that at 3000rpm approx that the motor gets a bit fluffy/uneven and will not really allow me to go any further without really booting it.
Do we think that this could be to do with timing or carb settings?
I can adjust the timing from inside the car whilst driving ,either advance it or retard it.
Muscle Manta and a few other friends came down to help set the motor up and it all seemed good.
We have lighter springs and different rods in as per MM's set up.
Any advice or thoughts would be good.
Cheers
Paul

Vacuum or mechanical secondarys?
Mike

Hi Mike
It's a Webber 500 so mechanical secondaries I believe
P

It sounds like the carb, as the secondarys start to open it is going lean, could be the secondarys opening too soon/quickly or it could be not enough accelerator pump action.
Best regards
Mike

Mike
Would this imply that I need to extend the accelerator arm as has been done by the likes of Sidecar and MM? or do I need to play with the rods and springs again?
Thanks for your help already.
Cheers
P

Paul,

What size engine and spec, and what jets, rods and springs are you using?

Kevin.

gelmonkey wrote:Mike
Would this imply that I need to extend the accelerator arm as has been done by the likes of Sidecar and MM? or do I need to play with the rods and springs again?
Thanks for your help already.
Cheers
P

Paul,

My pump arm is no longer extended, this is due to the fact that I've modified the air valve that sits above the secondaries so that it opens quicker than standard. Because of this I need quite rich shot from the pump.

I've found that the secondary jets were way too big on my engine. I had to make a set of 66 jets in order to get the AFR right. The smaller 3.5 engines that I've worked on seem to need bigger secondaries, around 83 in size.

I guess what we need to know is the following:-

1. Engine size
2. ignition timing, static, full advance and at the RPM that its all in.
3. Vac advance, is it fitted
4. The carb setup, primary jets, rods, secondary jets, pump arm hole, pilot screws.

Off out fishing now, catch you later!

EDIT...Kev you posted as I was posting the gumph above!

Pete

Hi Paul
I was implying increasing the stroke of the pump, most likley by extending the arm, however I will back out here as I was just working on theory and other unrelated carbs. I'll pass from here on as these guys know this carb.
Best regards
Mike

Hi Guys
From the info that I have written down it seems most likely that we set the carb up to MM's spec which is as follows...

1 stage lean using 86 primaries and 92 secondaries.
We have used 6755 rods....
The full advance is in early but I cannot remember (not written that bit down) how early but may be as low as 2500rpm or sooner.

Pump arm set at lowest hole.
Vac sec is fitted but not locked.
Engine size is 4337cc

Ignition timing set IRC as standard.Can be adjusted from inside the car via a dial.
Cam timimg 4 deg retarded.

Not sure what info you need regarding the pilot screws.

Bear in mind that we have set the engine up for MM's 3.9 so am sure it is a bit out on all the settings.
Cheers
Paul

Paul,

Sounds like you have a similar engine to mine 4.2 +40 thou. except I have modded Buick 300 heads and I assume you have Rover heads.

Three more questions, what spec heads and what cam and is it a performer manifold?

Not sure what you mean by vac sec fitted but not locked, are you talking about the dizzy vac advance unit, Both Pete and I run with it disconnected because the Edelbrock pulls far too much vacuum for the lucas dizzy.

Also did you change the step up springs on the rods from standard?

Kevin.

If you have a 1404 weber 500 I think its vac secondaries. In which case the accelerator pump is only on the front bores.
Secondaries only get what they need depending on carb signal. Can you measure manifold vacuum at this fluffy point? Ideally tack on a gauge and get someone to log vac up to ther fluffy point and then in it and then after it when she picked up.

Pel

Hi Guys

Kevin..heads are TVR Tuscan Challenge heads, Kin How Much
Cam is RS Typhoon
Manifold is performer as you suspected.
Springs have been changed irc down one step.
Dizzy is Mallory Magnetic with advance connected and not locked out.

Perry.. of course it is vac secondaries, was talking poo earlier.
As for a vacuum gauge the only one I have access to is Mrs Gelmonkey telling me ,"You've missed a bit"

Thanks due to all who are helping me with this so far

Cheers
Paul

Paul,

The jetting you have is identical to the set up in my engine but I changed to the silver step up springs as before the change it would not idle at under 1500RPM, now it is comfortable at 1000 RPM and would possible idle lower but with a new tight engine I am happy with the higher idle

The Typhoon cam is very (suspiciously) similar to the Crower 50232 I have so your jetting should be close to ideal although each engine may need fine tuning for best results.

The Edelbrock 500 1404 seems to have both mechanical and vac control of the secondaries in that the butterflys are mechanically controlled, but the flaps at the top provide an element of control to only provide the flow that the engine actually needs which is quite clever.

Do you know the actual spec of the TVR Challenge heads. ie valve and port runner sizes? if not I can check with Paul at Castle Race Engines as he built quite a few engines for the race series, I suspect that they may flow more than my mildly modded big valve Buick 300 heads.

The Mallory is quite simple to set up as the advance curves are given in the spec sheets and you can adjust the Vac unit, if you want to run with vacuum set it to no more than 5 Deg. which may give a few more MPG.


Advance curve sheets if you do not have them.

http://www.malloryperformance.com/pdf/29014.pdf

Ideally a 4.3 engine should be all in at 32-34 deg. at around 3000 RPM which unless you reduce the mechanical advance which is 24 deg. means setting the initial advance to 8-10 degrees with vac disconnected. I would suggest this as a baseline although some engines respond better to more inital advance for better response at under 3000RPM, above 3000 RPM the dizzy is of course at full advance all the way to the red line.

Can you describe the fluffing in a bit more detail, is it on a steady throttle when accelerating or when you suddenly put your foot down. does it clear again once past 3000 RPM.

What colour step up springs have you fitted, I would be tempted to try the silver ones as it's only a 10 min. job and see if that cures it, if no improvement then try the pump lever in the middle position which from memory is where mine is.

Interesting that the problem is at 3000RPM as this is where the cam is coming on song and there will be a leap in fuelling reqirement, if you have the wrong step up spings the carb will not stage to rich and won't be supplying the correct fuelling.

Whats the idle like?
Kevin.

Paul- is it all the time (once up to running temperature) or does it get worse as the engine gets warm (proper warm not just coolant temp)?

Hi All
Answers to the questions then.

Idle rock steady at 800rpm once warm.
Silver springs fitted.
Fluffy when blipping loud pedal and also on steady acceleration into 3k.
Will go through 3k but not really happy about it.
Feels like a misfire.
Dont know the full spec of the heads but can tell you they have 1.61" inlet valves and slightly smaller ex valves.
Don't know if this is any help but they have triple grip steps on the collets.
Probably no help at all that bit really
My ignorance of this carb is high as you can tell which is why
I had help setting it up in the first place.
Give me a set of 45's and happy as a pig in pooh,the 500 however......

Thanks for the help so far
Cheers
Paul