1776 tuning advice - What carbs are you using?

[Zcat7]

I've had a few false starts since building this engine but I think I'm nearly there... Now I just need some advice to get rid of the last few niggles

http://forum.earlybay.com/viewtopic.php?f=2&t=53981

I have dual Kadron/Solex 40s, which were perfect on my old 1641. I got a jetting and venturi pack from Kaddieshack (apparently the experts in Kadrons) which is supposed to match the new config - 1776 with standard heads and Engle 100 cam and SVDA with the vacuum from the left carb (they say its a very common setup).

The problems I have now are some stuttering just off throttle/very light throttle which seems to get worse with engine temp (makes cruising at 30 very irritating). Even on the drive if I rev to about 2000rpm the engine kind of makes a "fuffling" sound, which goes when you throttle up or down. Also I previously had to adjust the accelerator pumps to max to get it to rev freely without hesitating and thought I was done with that. I then took it for its longest high-speed run since the rebuild the other day. The temperature gauge settled on 220 when cruising at 3500rpm, which I thought might be a bit hot. Previously, on country lanes on a hot day, it had settled on 180. But now, as it it gets hot, it starts to falter a bit on hard acceleration, which twinned with the stuttering makes it all a bit annoying. I backed off the timing a bit as it was over 34 degrees max advance. Now its 30 deg at 3500 revs, vac connected. This seemed to improve things but it hesitates a bit again when revving now...

The engine feels and sounds so good in all other respects (starts on the button, ticks over nice etc) and does accelerate strongly through most parts of the rev range so I'm convinced that its just fuel and/or timing. I just need to smooth these niggles out but am not sure where to go now.

So -

Could the jetting be wrong? I have adjusted mixture several times and the acc pumps are maxed
Is the timing wrong?
Could the vac advance curve be wrong for a 1776 with that cam?
Would I be best putting the old 009 dizzy back?
Could the plugs be too cold/hot? (I'm using NGK BP5ES)

 

[Jolly45]

Hello Zcat,

I'm no expert, but it sounds to me you need to get it set-up on a rolling road.

Jack.

 

[rlepecha]

Is it an svda dizzy? You need to set it at 30 degrees Max with VAC disconnected if it is.

 

[jonboylaw]

Vac will not make much difference so long as the throttle is steady. Sounds like the idle jets need upping a little. Does it pop or hunt on tick over? Also check the linkage to make sure both carbs are opening equally and are balanced.
Other than that, check the points gap and then swap the coil for a known good one. If all above ok, start looking for air leaks.
I don't know solex carbs myself, running DRLAs which are pretty simple to set up.


Sent from my GX64 SatCom phone using Tapatalk

 

[Zcat7]

Thanks guys. From what I've been reading elsewhere I think Johnboylaw could be right in that the idle jets need upping. It does pop and crackle a bit when cold but I thought that it just needed warming up (no choke...). However it didn't used to do this in 1641 trim... The problem is that the jets I got from Kaddieshack had all the numbers filed of because they ream the jets themselves. What they wouldn't tell me, despite repeated asking, was the new jet size (which is effing irritating...), simply saying instead "don't worry, they will be the right ones, we do loads of these.." :roll:
So it appears that these engines run mainly on the idle jets because everything is done below 4000 rpm (idles deal up to about 2500-3000 rpm) and that you can get the accelerator pump to counter things a bit in certain areas but if your idle is too small then you're going to run lean and hot. so, looks like I'll have to find an aircooled rolling road expert in the area who has a stock of Solex jets or splash out for a few myself and start experimenting.

Johnboylaw, to answer your questions:

Ticks over pretty smooth I'd say, maybe the occasional little hiccup which I put down to the robbed vacuum effect of the single barrels. Certainly better than its ever been though even in 1641 form.
I've been fastidious about the linkage and balancing, went round and round quite a few times on this.
The dizzy is running an Accuspark module so no points. the coil is a Flamethrower and is pretty new (especially mileage wise).

I did wonder about the Accuspark module as this thing gets mighty hot (by design apparently) but I wondered if it might be breaking down at high temp? I have a Pertronix in my 009 and in fairness never had a problem with it.

 

[jonboylaw]

Lean idle will pop and stutter all the time, not just when cold. You could always get a set of jet drills and try that way, however Kadieshack are standing behind their selection so you may want to put that to one side for now. You could check the jets /idle circuit for blockages just for completeness.
Do check the base plate on the dizzy is freely moving and that it rotates with a vac signal applied (suck the tube). Also check the dizzy cap/rotor condition.




Sent from my GX64 SatCom phone using Tapatalk

 

[Zcat7]

So I've been doing more research on carb jetting and also spoke to a guy at The Carburettor Hospital (pretty local to me) where they deal with all makes of carb for cars old and new.

First I found a guy on The Samba who had built a 1776 with the same cam and carbs as me, stock heads etc but single port and with a 009 dizzy. He is running 55 Idles and 130 mains, which were the very things I took out of my carbs in lieu of the Kaddieshack ones...! He quotes:

...I just started up and put about 300 miles on an older 1776 engine I built a few years ago, single port stock-valve (35x32) heads, Engle 100 cam, Kads (130 mains, 55 idles), Scat linkage and aircooled.net new US-made 009 distrib. After minor coughing when stone cold, it runs surprisingly smoothly with no flat spots.

Interesting...

Then had the guy at The Carburettor Hospital had a rant "Oh those bloody carbs! Terrible things, nothing but trouble (yeah yeah yeah... :roll: ) Can't help you, don't do jets for them and you won't find them in this country". But he went on to say that if going up from 1641 to 1776 he wouldn't bother changing anything, maybe just up the mains a touch say 130 - 135! So 2 people in agreement on jet size...

So I took the idles out today to check them against my 55s and found that the holes are about twice the size (remember they aren't size marked...)! Bearing in mind (from what I've read) 55 means .55mm then I reckon I'm looking at a pair of 99s. So I swapped them out for the 55s, reset the mixture, re-timed back to 30 degrees vac off (thanks rlepecha) and it transformed the engine.

The "fluffling" around 2000rpm has gone completely. I can pull away normally without having to over rev it and I can cruise normally. It's not quite perfect but soooo much closer that you'd hardly notice a problem. In fact the only problem is that it doesn't seem to like it around 1800 rpm in high gear where it gets a touch stuttery rather than just struggling and on a couple of occasions, after I had decelerated into a bend, it faltered before picking up if the gear was a bit high. But only for a second. I think I might need to recheck the accelerator pumps and take a look at those mains... I'm also going to investigate the fuel pump (electric) as I have had a similar feeling problem on another car where it started to fuel starve after cruising at speed and then demanding an acceleration spurt.

Jonboylaw - I had rebuilt the dizzy before fitting but checked the baseplate today. I could advance and hold the revs by sucking the straw so assume all is good. Cap is new.

Sorry about the ramble but I thought it might be useful info for someone going through the same issues!

 

[Mr Brightside]

I have a similar spec engine & had slight hesitation around 2,000 rpm. Upping the pump jet (mine are DRLA40's) from 45 to 50 cured it.


Sent from my iPhone using Tapatalk

 

[jonboylaw]

Good progress. I run 60/130 in my 36 dells (1955cc) so very close.

Pull a plug and see what the plugs are like.


Sent from my GX64 SatCom phone using Tapatalk

 

[Zcat7]

Think I've sorted it!

Plug check indicated that it was running a bit lean... I checked the accelerator pumps and couldn't get any more squirt out of them. I also spent time setting the nozzle squirt direction and checking all galleries were clear. No change.

Then it occurred to me that by upping the venturis to 30 from 28 I would have effectively weakened the mixture as the 55 idles were matched to 28s. So I swapped them out and now have the original idles (55), original venturis (28) and a richer main (looking at the hole size probably a 135). I reset everything and it now runs really quite sweet. Nice even tickover, strong pickup and any stumbling that might occur is now more of a "struggle" and is down at around 1400-1500rpm in 4th gear, where its entitled to struggle! I took it for a long run around country lanes and long sweeping roads. It pulls hard in 4th at WOT until I back off at 4000rpm. Temperature settled at a touch over 180 on the gauge it cruised smoothly throughout the rev range (though I didn't do any full throttle motorway cruising yet).

So what do I do now? Enjoy it as it is or aim to up the venturis and idles? I only say this because I have the notion that the engine feels slightly strangled with the narrower venturis but that could just be me over thinking it all and letting my imagination get involved! I know my earlier calculations suggested a 30-32 venturi but I don't know enough about carbs (yet!) to decide.

One lesson that has come from this is that using unmarked jets is a minefield. Kaddieshack seem to have a good reputation, especially on The Samba, but frankly what they sent me sucked large. Hopefully this config is a good baseline from which to work. Whatever I decide it's been a good learning curve!