[James408]

Hi, I'm experiencing what I believe to be detonation in third gear on my 400, I cant hardly keep it on the road the power is there but when I hit 3rd gear it starts to clatter. The only changes I have made is a Continental 3200 stall and replaced the Holley 3310 with a Quick Fuel slayer 750 w/vacuum secondaries. I'm using a Carter Super Street pump. I have a unilite dist. with it setup up with 16 initial and 36 total. I have not checked the timing again.

Will fuel starvation cause this? I will back the timing off to see if that helps. thanks

[grandville455]

Same jetting as other carb? All bolts tight on convertor? Proper clearance?

[Blued and Painted]

The vacumn signal to the advance may have changed.

[James408]

Yes, actually, this carb has bigger jets than the holley. converter is fine.

No vaccum advance. Mechanical advance only distributer.

Will running lean cause detonation?

[geeteeohguy]

Running lean can absolutely cause detonation. Lean engines run hotter and are more prone to detonation.

[HWYSTR455]

Iron heads, may want to drop back to 32* instead of 36.

Could be a bad tank of gas too.

What plugs are you running, and what do they look like.

Same power valve as previous carb too? What's your vacuum at idle, and the power valve you're running?

Might as well list the jets you're running too while you're at it.

Explain 'can't hardly keep it on the road' ?

.

[James408]

The motor runs cool..

I'm running Autolite 85s....haven't checked them yet on color
yes...same 6.5 pv

running 72 primary jets and 82 secondary jets. was running in old carb 72/75

I'm sorry I meant it has a lot of power and keeping it on the road while spinning through 1st and 2nd means keeping it out of the ditch.

first thing I'll do is back off of the timing.

[HWYSTR455]

Does the new carb have the choke horn milled off? You may consider stepping up a size or two on the primaries.

Yeah, back it off a little, see how that does. Limit the advance, don't back off initial. You have the key for setting the advance on the unilite, right?

.

[James408]

No it still has the horn. ok I can try that. but I'll jack with the timing first.

no this does not have the key it has the tab I have to bend to limit the advance which is no prob. I'll back it up first to see what it does. thanks!

[James408]

ok backed timing down to 32 total....still some clatter.....also after Ive run it away and I go through all through gears, I feel like I'm not getting the fuel and I hear clatter....is this possible vapor lock and a lean condition making the clatter? Gonna put my old 3310 on and see if it does that.

[HWYSTR455]

Yeah, vapor lock or lean can cause det. What's your fuel system like?

.

[James408]

I'm running stock 3/8 fuel line from tank to fuel pump and 3/8 steel braided line to carb. Fuel pump is carter super street m6907 mechanical pump. Car does not overheat but struggles and clatters in third gear.

[ponjohn]

Did it improve with less timing?

Do you run 93 octane?

Did it do this before?

[wrench]

When does this happen? Cruising in 3rd, W.O.t.? It didn't happen before the carb and converter change?

[James408]

no, this happens shifting wot through the gears....not wot cruising in third. No and I had no clatter with my timing bumped up to 36 total and before the converter and carb change. I also changed the converter and carb at the same time. Is it worth taking the quick fuel off and putting my old 3310 on it...the 3310 has a main body that is an original 780 main body with down leg boosters and choke horn milled off.

It helped a little backing the timing off. but if it was detonation from too much timing wouldn't it do it all the time like in drive or 1st and 2nd gear at wot.....with my old combo with cheap 2800 stall and 3310 it did not clatter at all at 36 total.

[kyle_blake]

From what I read the slayer carb float level adjustment requires a higher setting thus more fuel is in the bowl versus the holley which sets float level lower. Since it's from a stand still WOT and at the end of the "run" sounds like timing/fuel is culprit.

I wonder if fuel pressure isn't enough after those upgrades? From the way you describe it's a whole lot of fun out of first and second!
Let me know how the 3310 works out after going back it .

[dmac]

swapping the carbs will at least tell you if the carb is the problem.

[James408]

yeah Kyle, the floats are set higher, on the primary and secondaries I have the fuel level set just above halfways on the sight glasses. Hell maybe it needs more IDK. but yes the car is really responsive and fun and has a crazy second gear now. I will swap carbs this weekend and report back. thanks guys.

[steve25]

You need to take a vacuum reading and note when the detonation starts to creep in.
Just because you have fatter jetting, that is more for full throttle mixure, the vacuum reading will tell you if you need a different power valve for the correct part throttle mixture.

[Cliff R]

Not nearly enough fuel delivery for what you are doing. Those Carter pumps aren't that great right to start with, and nowhere near up to their full capacity sucking thru tiny stock fuel lines.

When you took steps to make the car faster with the better converter, the acceleration of the vehicle makes the mechanical pump even harder pressed to keep the carb full on hard runs.

As far as carb jetting goes, you can't compare jetting between two completely different units. The metering blocks, airbleeds and type of boosters are major contributors to how much fuel is actually delivered to the engine on hard runs.

I would be upgrading the fuel system, reducing the timing, and throwing more fuel at it till it quits pinging at full throttle. It doesn't take too full throttle runs with detonation to pound down the rod bearings, break piston ring lands, and breach head gaskets......Cliff