DCOE/Cannon rich&lean

[Speedracer906]

 Well, I looked around and came up short of a thread that spoke of my issue. I’m sure it exists...

I have a DCOE mounted to a Cannon intake on my l20 powered 620. I’m getting real close on my tune of the engine, I’m doing it all by feel.

I do know I’m up in around 12-14 degrees of advance on my timing, I’m not running the vacume advance yet. 

My question is: cylinder 1 & 4 burn good to lean, and Cylinder 2 & 4 are a bit rich. I imagine that the longer runners on my Cannon intake mix the fuel better than the short runs, right? I was wondering if a hotter plug on 2 & 4 could help? I also wonder, if by chance, my valve adjustments happen to be off a smidge and coincidentally coincide with 2 & 3s rich-ness. (I adjusted the valve cold)  

lastly, I need to find a fitting thet can screw to my only existing vacume port, on the cannon, so that I can steal a vacume advance line for my distributor. It would have to work the brake boost line and have a small fitting for the distributor. 

Thanks.

[datzenmike]

1&4 2&4? I imagine you mean 2&3? That would tell me that the 2&3 barrel jet is too large.

 

Your vacuum advance only affects part throttle and your distributor is set for a ported vacuum source. Connecting to intake will supply a huge vacuum signal at idle and part throttle and run the advance way up and probably ping all the time. You will likely have to retard it a lot to be drivable... and then the over all advance above 3K will be much less that the optimum 32-34 degrees. I think there are adjustable vacuum advance units that you can tailor to your needs.  

[Crashtd420]

Is this a single dcoe?

[Stoffregen Motorsports]

Mike, I have seen adjustable advance units on BMC motors, and on early American engines, but I have not seen one on a Datsun.

 

The best way to ensure you have the proper, safe amount of distributor advance is to re-curve your distributor. You can do it at home with a welder and a file, with hard to find Nissan Motorsports parts, or send it off to someone that can do it for you.

 

 

[Speedracer906]

Darn it, yes Mike, I meant 1 & 4 and 2 & 3. I only have 1x DCOE. 2 & 3 are running richer.

I’m not sure I need to run any vacume advance, but if it was possible I thought I would. 

[datzenmike]

20 hours ago, Stoffregen Motorsports said:

Mike, I have seen adjustable advance units on BMC motors, and on early American engines, but I have not seen one on a Datsun.

 

The best way to ensure you have the proper, safe amount of distributor advance is to re-curve your distributor. You can do it at home with a welder and a file, with hard to find Nissan Motorsports parts, or send it off to someone that can do it for you.

 

 

 

Sorry, didn't mean Nissan made.

 

Re-curving? Like removing some of the mechanical advance to compensate for the added vacuum advance at lower speeds but keeping overall total advance? Wouldn't it be easier to lessen the advance tip in point and limit it? thus keeping WOT advance the same?

 

 

1 hour ago, Speedracer906 said:

Darn it, yes Mike, I meant 1 & 4 and 2 & 3. I only have 1x DCOE. 2 & 3 are running richer.

I’m not sure I need to run any vacume advance, but if it was possible I thought I would. 

 

Not that familiar with the side drafts but does not cylinder 2&3 draw air from the same side of the carburetor?

 

Vacuum advance tailors the ignition advance according to engine load. Heavier throttle (more cylinder filling needs less) light throttle and cruise (weak cylinder filling needs more advance) Vacuum advance improves drive ability and mileage.

[Stoffregen Motorsports]

There's three parts to setting the curve of a distributor:

• amount of mechanical advance
• hard stop on the high limit
• rate at which the timing advances

Yes, I do remove some internal pieces, but that only means removal of one of the two springs holding back the distributor cam. And you need the hard stop at the top for the engine's safety. I do this by shortening the slot with a tiny bit of weld. There used to be a SSS distributor cam from Nissan that had the shorter slots already, but I don't think they are around anymore.

 

Lessening the tip-in point, as you say, is the opposite of what the L motors love. They need more timing at an earlier time than the stock weights and springs allow, which is why I remove one of the springs.

[Crashtd420]

2 hours ago, datzenmike said:

 

Not that familiar with the side drafts but does not cylinder 2&3 draw air from the same side of the carburetor?

 

If he has a single side draft and cannon intake, 1 and 2 are paired and 3 and 4...

By looks #1 and #4 are slightly longer runners, but not by much....

Probably looks like this...

 

[datzenmike]

Ahhh… thought separated. So basically like the stock intake.

[Speedracer906]

Yup, 1 & 4 are longer runs for sure. So since jet changes are not an option, can a hotter plug on 2 & 3 help to clean up the burn? Maybe I should just try it. I thought I’ve heard that some intakes have issues like what I’m experiencing. 

Sorry I checked out a couple days there, work was a bit comanding this last week.

[datzenmike]

Could the 'dirty' plugs be from burnt oil? from worn valve seals? Does it puff any smoke on cold start up?

[Speedracer906]

no, but I mentioned that my valve adjustment was done cold. Should I check that you think?

[datzenmike]

Never hurts. Hot is where they run. A cold setting assumes that the clearances open up the proper amount.