Venturi Size for 36DRLA 1641

[Ghia Nut]

Ok, so I got to finally tune the carbs today using the german snail tool for aircooled.net the damn thing is worth its weight in gold.

While I was rebuilding the carbs I ordered a set from alfa1750
I went with his listed suggestion of 33 pump jets, and bumping up the venturi to 30mm as I have a 1641.

The pump jets were way too lean so I put back in the 50's.

I tuned the carbs via aircooled.nets carbs 103 and it idles awesome.

I am having some issues in transition though. It feels like it is missing right from 1500-2300 rpms a bit.

Would switching back to 28 venturis help this?

Timing is spot on. I havent adjusted the mixture screws quite yet.
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'59 typ1 rajay turbo
'72 Ghia rajay 1641 dual 36DRLAs, 1 3/8" SS merged header and fat boy
78" GL Vert with ej22t swap
This will likely change tomorrow to something else.

[jfats808]

List jetting and specs.
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2276 IDA's 86C 11-1 DD

[modok]

Low rpm flat spot is due to the big valve heads somewhat.
yes 28 would be good for the engine size but then what is the point of the BIG heads??

Just have to tune around it best you can. I bet more advance at those rpms would help but you have to change/modify the distributor so the total advance is not too much.

[Ghia Nut]

Specs
1641
Heads are 40mmx35.5 standard 85.5
DVDA distributor, max advance 30-32* at 3k rpms, think I set it at 32,
didnt have vac advance hooked up when I did this.
stock stainless steel dansk with pea shooter exhaust.

Carbs are dell 36drlas
180 Main Air Correctors
9164.2 Emulsion Tubes
122 Main Jets
55 Idle Jets
50 Pump Jets
Vent originally 28, now bumped up to 30.
_________________
'59 typ1 rajay turbo
'72 Ghia rajay 1641 dual 36DRLAs, 1 3/8" SS merged header and fat boy
78" GL Vert with ej22t swap
This will likely change tomorrow to something else.

[Danwvw]

I am running 30's ok on mine but I think the idle jets may be 60's. Mine was kind of missing until I set the floats to produce the same amount of gas in the bowls. I plan on using 28mm jets on my next engine so if your done with yours send them to me!
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1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[Alstrup]

[Ghia Nut]

[Ghia Nut]

also, I chose these heads back when I was set on going turbo, but the turbo is going on another car so yeah :/
I dont track the car, or drag it. I will get into it every once in a while but I dont drive past 4k rpms usually.

I just want a nice strong engine.
Id eventually like to build a nicer engine for it one day, but I really just want to enjoy and maintain the car now.

P.S. Non ethanol fuel has made a LOAD of difference, I dont think its ever run this good.
_________________
'59 typ1 rajay turbo
'72 Ghia rajay 1641 dual 36DRLAs, 1 3/8" SS merged header and fat boy
78" GL Vert with ej22t swap
This will likely change tomorrow to something else.

[jfats808]

I agree with keeping the 30 vents. I suggest trying out a 58 idle. A bigger air wont help atm since your stumbling at 1500. Id bump mains to 125 and retune, then take a drive and report back. A better flowing exhaust would make a world of difference. Till an exhaust upgrade, it will be a lot of jetting fine tuning to make it work. Tune and time the vac adv.
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2276 IDA's 86C 11-1 DD

[Dan Ruddock]

Stock cam? Ratio rockers would also be a good idea. Dump the exhaust.

Dan

[Ghia Nut]

Extractor style exhaust is ordered. Decided on the MA stainless steel with fat boy. I know the collector isnt as long, but Im sure its better than the current muffler and pea shooter. Once thats on I will tackle tuning.
_________________
'59 typ1 rajay turbo
'72 Ghia rajay 1641 dual 36DRLAs, 1 3/8" SS merged header and fat boy
78" GL Vert with ej22t swap
This will likely change tomorrow to something else.

[Alstrup]

OK. I see your point, but I am not that fond of "step by step" improvements on engines. It almost always creates bad issues, because the parts do not interact that well. This is one of these cases.

I can help you make it run a good deal better. Perfect (?) no. Better.

1. Increase idle timing to 10 btdc and reduce max advance to 32 btdc at approx 2800 rpm. With vacum should be around 38-40 max. Then turn the idle mix screws 0,25 to 0,5 turn inwards, dependant on what it likes.
2. One of your problems are that since you have so low CR the vacum signal to the carbs are weak. You should make 4 rings with 40 mm I.D and grind them to fit into the manifold on the carb side, to reduce the amount of mix in motion. That will improve the vacum signal and make the engine more reponsive.
3. Dave´s suggestion on jetting may come in handy. Again, you need "more jet" because of a weak signal.
4. Good on the exhaust. Dont know MA I dont think, but it can only be better than the stocker. The fat boy MAY actually be too free flowing, which will increase the off idle stumble. If that happens you can install old model 1200 rockers (1-1) on exhaust alone, to reduce the overscavenging. In fact I think it is rather certain that you will get that problem, so I would do that so you have one proble less to fight.

T

[Ghia Nut]

Thank you guys for the help, this is an interesting problem though which is something I have never dealt with before, but its fun

MA is mid america. Apparently its some what uncommon to find 1 3/8" merged header in stainless, I prefer stainless as it just lasts longer. I understand the idea of ceramic coating, but trying to get a good ceramic coating is expensive, I really dont want to buy a mild steel exhaust, only to have to ship it out to get professionally done and spend more money on coating or shipping. Ceramic bothers me as it potentially chips as well. Any who this is the one Im speaking of.

http://image.mamotorworksmedia.com/imageproc.aspx?...&w=369

http://image.mamotorworksmedia.com/imageproc.aspx?...&w=369

Alstrup, thanks for the advice, its much appreciated and I will tinker with it some.
I didnt even think about vac being affected with these heads, I knew port velocity would be affected but not so much that it would effect vacuum pressure, then again, more flow lest vacuum. I may take some readings off of the vac to see what I get in terms of vac pressure. I do have ported vacuum which is right at the throttle plate, so at idle no vacuum, open throttle the distributor sees vacuum. I dont know what pressure is required to operate the vac advance distributor, for some reason 5lbs rings a bell, I rebuilt it and the vac advance is working properly. I do know that.

I do also happen to have CB's black box and a locked bosch 010 sitting on the shelf for a turbo project as well, so I can potentially use that to adjust timing to counteract this.

There is also another question I have in regards to the air bleed screws on the dellorto. When I tuned the carbs, I had to adjust down one side of the throttle of the carbs to match the other. Aircooled.net suggests

[Alstrup]

4 is about right.

[Ghia Nut]

Just a report on the car. Got the 1 3/8s on and the muffler. Noticed she was running a bit hotter than she was. Still idles fine no popping there. It will pop back through exhaust when shifting but only once. I'm going to order the 125 mains, if I'm not having an issue at idle do I still need the 58?

Also putting on cb black box to help with ignition. It did seem to have a high rpm miss at 3k plus which I think made it rrun hotter.
_________________
'59 typ1 rajay turbo
'72 Ghia rajay 1641 dual 36DRLAs, 1 3/8" SS merged header and fat boy
78" GL Vert with ej22t swap
This will likely change tomorrow to something else.