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Edelbrock rpms

T

themons

Member
Hello everyone:

After successfully installing my 1409 Edelbrocks, I have discovered that I have a serious problem.

I cannot get either engine past 3000 rpms. This translates to about 11.5 knots. In addition, my fuel consumption is worse than with my original quadrajets so I don't think I'm getting on plane.

Any ideas?
 
With the engine off, manually work the secondaries, making sure they are not hitting the gasket or adapter plate, wedge, etc. These are at the bottom of the carb.
 
Of course you had someone operate the lever while you watched the carb to be sure the darn thing is opening all the way, yes?
 
shouldn't need an extra set of hands to verify the throttle plates open.

With the throttle plates wide open, you have an opportunity to get the required air into the engine. Now I'd check to make sure the air valves open due to the air flow going into the engine. There's no tension spring to adjust and I believe the weights are fixed. If they don't open with the engine under load, I'd start looking for a binding shaft, interference with the weights, etc.

If the air valves do open under load, I'd make sure the ignition timing advances to full?
 
Have you noticed lately that therre seems to be an increase in the postings regarding FULL TIMING ADVANCE ? Do you think it is merely aging of distributor mechanisms or maintenance issues?
 
I think it just correlates to the issues being posted. That said, it took me a while to add that to my 'checklist' for the spring ritual....like they say, the more you learn, the more you realize just how ignorant you really are.
 
I talked to Summit Racing tech support.

The guy said that if the secondary air valves open too quickly that the engine will not increase in rpms.

But there is no way to adjust the weights to control the valves?
 
This is on BOTH engines? really odd. Did you wire in the electric chokes to a full 12v source? Did you verify that the chokes are fully open after a couple minutes? I have these same carbs, and have had to do nothing to the secondaries, ever, for 10 years now. i can jam the throttles wide open, and not even a hesitation; once in a while, i can get a backfire when I do that, though. I could try a stronger accelerator pump setting, i suppose.
 
Yes, this happens on both engines.

I have tried both the 12 volt choke connector and wire tying the choke open. When connected to 12 volts, it take a minute or so to open up.

The air valve for the secondaries apparently have no linkage to anything and are only controlled by the vacuum and the weight.
 
There's no reason why the secondaries need to be modified on those carbs. Your ear will tell you when they open up, or a helper can eyeball the throttle shaft to see it move. Booting a good one in neutral will also open the secondaries.

You say mileage and power are way off. Hummmm... Not sure what's going on here. Could you past a photo of your setup?

Jeff
 
The tech at Summit doesn't know that carb very well. If they open too fast, you'll get a lean bog or, like DD indicated, the lean backfire.

The throttle valves open and then the pressure differential (vacuum) will open the air valves. Like Jeff said, the sound change is hard to miss. I've only seen one that was modified and I'd label that minor (on a street racer).

either way, I'd still make sure the timing advance is working.
 
Makomark:

I just saw your PM today.

As it turns out, just yesterday, I got a timing light and checked the settings. Turns out it was 20 degrees at idle and 40 degrees at cruising rpms.
I reset the idle to 10 degrees and am going to test it out tomorrow. Thanks for the earlier suggestion.
 
themons said:
.............. As it turns out, just yesterday, I got a timing light and checked the settings. Turns out it was 20 degrees at idle and 40 degrees at cruising rpms.
I reset the idle to 10 degrees and am going to test it out tomorrow.
Click to expand...
Something is fishy about 20 advance at idle rpm. Most engines, when warm, will not even fire with this much spark lead. They will "buck" against this much ignition advance.
And the 40* TA @ cruise RPM is a recipe for detonation!

  1. Are you by chance using a digitally advancing timing light that may not be set to standard strobe mode?
  2. Is your harmonic balancer properly marked off for checking TA in standard strobe mode?
This would indeed appear to be odd (especially on two "like" engines) when only a carburetor change has been made..... if I understood you correctly!

One further note regarding the low rpm issue....... if ignition advance were to fall short of a correct TA, then the symptoms would be very similar to what you have described!
Example: a TA of only 20* @ 3k rpm, when the TA should actually be 28* @ 3.2k rpm (again, example only!)
You may want to pull out your OEM manual and see what is spec'd out for TA, and at what RPM.


knuckle47 said:
Have you noticed lately that there seems to be an increase in the postings regarding FULL TIMING ADVANCE ? Do you think it is merely aging of distributor mechanisms or maintenance issues?
Click to expand...
I can't asnwer that question per se', but I've spoken with many seasoned mechanics that do not give this enough consideration.
In my book, this has always been extremely important for a marine gasser!
 
Last edited:
Changing the timing at this point only adds another variable and makes the problem solving more difficult. If it ran properly with the Quadrajets at 20 degrees initial advance, it should do the same with the edelbrocks. After reading all the posts, I am still not sure that I you confirmed that the throttles were fully open when the remote controls were pushed fully forward...is that the case? Were the carbs you ordered calibrated for the altitude they are to be used at??? Has there been any sudden marine growth on the hull between the period the boat was used with the Quadrajets and the edelbrocks??? The reduced fuel mileage is no surprise...if the boat is not planing, mileage will be terrible.
 
bobbyc said:
  1. Changing the timing at this point only adds another variable and makes the problem solving more difficult.
  2. Has there been any sudden marine growth on the hull between the period the boat was used with the Quadrajets and the edelbrocks??? The reduced fuel mileage is no surprise...if the boat is not planing, mileage will be terrible.
Click to expand...

  1. I respectfully, but fully disagree with that! This now becomes part of your P of E (process of elimination) whereby we go down each potential item, one ONLY at a time......., either finding or eliminating it as the cause! The P of E, if done correctly, will never let you down! Correcting ignition timing NOW will not harm the process!
  2. Now here we fully agree! Great question, and this needs to be considered!
 
Hi, quick question, which adapter plates did you use? on the instruction sheet, it specifies not to use an open plate adapter. My understanding is the 2 sides of the intake need to be separated. Something about a low vacuum signal due to air from 1 side effecting the other. I have 1409 and sat 1 on a stock manifold they don't align as the 1409 is a square bore and the stock was a spread bore. Also did you use the stock wedge plate to keep the carb tilted? I head the 1409 don't play nice tilted at extreme angles.

Let us know what you find, as I'm going to be running the same carbs, My motors are new waiting on installation, they have the performer intake, no adapter plate with the 1409.
 
No. I am using the bore adapter plate and the wedge. The change in timing seems not to be the problem. On top of that, my port fuel tank is now leaking.
 
Sorry to hear that. I put a 1409 on my 454 and it seems to work great. That said, it is on a 31 tiara so 3000rpm is 26 mph. It is out of the water now and to be honest I can't remember if I ever ran it past 3000 rpm. I'll have to be sure to run it full throttle and be sure. After you get your fuel tank fixed I guess you can put the old carbs back on and see if you get 4200rpm. Pain in the tail, I know but at least you will know for sure it's the carbs.
 
I put 2 new 1409's on my 85 270 crusaders and they work great. Only had to adjust the idle jets once. I will tell you it is the second set. The first set I got I had nothing but problems. Took them back to the speed shop where I got them and after a couple weeks of hassle with them and edlebrock they gave me a new pair. Come to find out that edlebrocks quality control is a little bit to be desired these days and bad stuff is slipping out. They did make it right though and I'm very happy with the performance and fuel mileage. I'll also tell you that I had to double my angle spacers to get them level. They just won't run at the same angle the Q-jets will.
 
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