View single post by Brett Gibson JH5 20497
 Posted: 05-23-2005 02:08 pm
PM Quote Reply Full Topic
Brett Gibson JH5 20497


Joined: 03-17-2005
Location: Hilton, New York USA
Posts: 736
Help, I’m still having Dellorto troubles and they are turning into nothing but a frustrating money pit that am about to give up on, and that really annoys me because I don’t normally like to throw in the towel.
History:            I picked up a set of Dellorto 40’s along with the manifold from England that were fitted to a JH over there, the jetting was factory stock so in my ignorance of Dell’s I thought they would work on my car due to it being a stock engine.

First thing I did was purchase rebuild kits, air cleaners, gaskets and hoses plus the linkage, then I stripped the carbs down and soaked them in a good quality carb solution overnight, I cleaned up and blew out all the passages and jets and made every thing spic and span, then I put them back together with all the new gaskets and O-rings, made a couple of silly mistakes, forgot to put O-rings back on the idle emulsion tubes and put the choke piston in the wrong way around so that it was on choke when it was supposed to be off, took care of that though.

Then I stripped the Stromberg’s off the car and modified the distributor, I removed the vacuum advance mechanism and locked the plate, and I use a flamethrower coil, 8 mm wires, NGK plugs, and an Allison electronic ignition, and the timing is 10 to 12 degrees advanced.

Once I fitted the Dell’s and got things running at idle they seemed fine but would pop and spit back under fast acceleration from 1000 to 3000 range, high RPM’s seemed fine, this is all taking place in the garage no road testing yet, well I made an earlier post and received some very helpful info on this problem it was recommended that I change some of my jetting, so here’s what I had and what I changed to,

new    old

40                    Carb Size

33         35        Choke Size

7848.1              Venturi

145       130       Main Jet

7772.5              Main Jet Emulsion Tube

190       160       Main Jet Air Correction Jet

55                    Idle Jet

7850.7   7850.5  Idle Jet Holder

45                    Pump Jet

70                    Cold Start Jet

7482.1              Cold Start Emulsion Tube

7298.2               Float Assembly

7481.2               Butter Flys

 The new chokes and items have reduced the popping and spitting but not eliminated it, my plugs still are very black and I get some exhaust pops and a little black smoke, all saying to rich, but I’m told to stop Dell’s from popping that I need to run richer.

I have tried a number of different ways to try and tune them in, first removing two plug wires and adjusting the mixture one carb at a time but that doesn’t seem to have any effect, then the other by hooking up a 4 vacuum gauge unit one to each carb and adjusting the mixture and air by pass screw to try and get the same across all, #4 cylinder always appears to be pulling more vac?? Still NG, then as with Strombers checking the air draw thru the barrel of the crab’s with a Uni-sycn type device and again the readings are all over and hard to get even close to each other, even trying all this it still pops and seems to rich.

I’ve looked over the carb schematic checking to see I didn’t forget some thing the only difference I can find is that I don’t have the spring/filter in the pump jets but I was told by JAE that it was not necessary, so right now I have taken the crab’s apart again cleaning and blowing out everything and tonight I will put it all back again and give it one more try, any and all suggestions would be greatly welcome like I said I don’t like to give up but in order to get to drive my car and hopefully make the East Coast Nationals I going to have to put the Stromberg’s back on if I cant get this settled ASAP. 

Thanks for reading all this. 

Cheer’s     Brett 

PS. I have good compression on all cylinders.