Setting up Dell 36's

[Graham L]

Anyone got any tips on setting up a pair of Dell 36's on my new 1641, swapped them over from my 1600 which ran fine but on the 1641 they seem to lack power and won't idle. Doing a quick read online it looks like I may need bigger main jets and chokes but not sure whats currently fitted to them without taking them apart.

Just wondered whether anyone had any suggestions tips on getting them to run better or at least idle, never used 36's before so a bit of a new one for me,

 

[K@rlos]

I definitely think it needs bigger jets, both mains and idle. I reckon the venturi's can stay the same though. It's only 57cc bigger but it will need more fuel.

Is the linkage opening both carbs equally?

 

[Trikky2]

I think its unlikely that an extra 50cc of engine capacity will require re jetting and would certainly not account for problems in getting the engine to idle.

Assuming all the other engine adjustments such as timing, advance mechanism etc are correct and you have also correctly synchronised the carbs; then your next step would be to check the carbs and manifolds for air leaks and/or dirt/blockages in the carbs themselves. Also check the fuel pump is not delivering too much pressure and causing the carbs to flood.

 

[K@rlos]

I had a set of 36's on my old 1600 that came off a 1500 which had 1300 heads opened to 1500 ( I don't know why ) and I had to go up a couple of jet sizes for that to run.

 

[Trikky2]

I had a set of 36's on my old 1600 that came off a 1500 which had 1300 heads opened to 1500 ( I don't know why ) and I had to go up a couple of jet sizes for that to run.

Wow - two jet sizes for 100cc? That does surprise me - I would have guestimated only one :lol:

I guess a lot depends on how the carb was jetted before eg. whether it was set a tad richer or leaner than ideal on the previous set up.

Back in the old days stock bays were set up with slightly leaner jets than beetles with the same engine. I never could figure why they did this but it was common practice back then to re jet bays to beetle specs which basically meant going up one size on main and idle jets and they did run smoother and lost their flat spots. :lol:

 

[Geeze]

Am with Trikky, 50cc extra shouldn't be enough to mean the jets are completely wrong (maybe touch lean but that's it) and symptoms don't sound like jetting :? .
Would start with the basics (timing, plugs, air leaks, etc) and try and get it to idle cleanly with the linkage disconnected before starting on changing jets. Though if the carbs have been off and laid to one side for a while, may be crud in the jets or just a bit gummed up.

 

[K@rlos]

I had a set of 36's on my old 1600 that came off a 1500 which had 1300 heads opened to 1500 ( I don't know why ) and I had to go up a couple of jet sizes for that to run.

Wow - two jet sizes for 100cc? That does surprise me - I would have guestimated only one :lol:

I guess a lot depends on how the carb was jetted before eg. whether it was set a tad richer or leaner than ideal on the previous set up.

Back in the old days stock bays were set up with slightly leaner jets than beetles with the same engine. I never could figure why they did this but it was common practice back then to re jet bays to beetle specs which basically meant going up one size on main and idle jets and they did run smoother and lost their flat spots. :lol:

Everyone has had different experiences with this old motors. Everydays a school day

 

[r73]

Ok with 36's you'll either have 28 or 30 vents
I think you'll roughly need
50 - 55 idles
115 - 120 mains
33-35 pumps
180 air correctors
#2 emulsions

You'll also need to set the float heights 5mm shut and 13mm open
They like 2.5-3 psi fuel pressure as well

Been a while since I did mine!

 

[Graham L]

Slight update been chatting to Dellorto today and they recommend 58 idles for the set up I have, forgot to mention it is running a Engle 110 and big valve heads.

Even they advise different mains between a 1600 & a 1641 even though its only 41cc, new mains/pumps & idles on order, rest of the bits look right

 

[Trikky2]

forgot to mention it is running a Engle 110 and big valve heads.

Thats rather vital info.

You would need to check jetting if you did this to a stock 1600. Carbs are not just about engine capacity, they are about gas flow. A very rough example would be :- At a given rpm a 1641 will draw around 3% more. Increasing the rpm from 4500 to 5000 will up the draw by 11% for instance.

It all gets very "comperlycated" which is why many resort to a rolling road to check the mix is right across the rev and load range.