Arnolt tuning specs

[Rich Slevin]

Looking for tuning specs for the Arnolt, timing, dist advance, etc. Also any help on setup of the Solex carbs would be appreciated. Thanks, Rich

[John Simmons]

Hi Rich,

If you send me your email address I can send you copies of the relevant pages from the workshop manual. What is the Chassis number of your Arnolt? The owners list that I have is not entirely up-to-date.

John Simmons

[Kevin H]

Jim McQuay sent the following by email ...

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According the Arnolt Bristol owners manual, the static ignition timing is set at 5 degrees before top dead center with the ignition fully retarded. Contact breaker gap is specified at .010 to .012 (A bit narrower than I am used to). Spark plugs were originally KLG P10L80 single piece. Substitutes are Champion Z9 or Z10, or NGK C6E or C7E (six is hotter than 7). These all are 10 MM plugs with 5/8 head size and 3/4 inch reach.

Again, the manual calls for a plug gap of .018 to .020. Also much narrower than I am used to. Even my 74 Norton has a recommended gap of .024 to .028

As for the carburetor adjustments, these should be minimal when operating below 3000 feet of elevation IF the original jetting is retained. There are two idle screws. One controls the engine speed at idle and should be set at 750 to 900 RPM. All three carburetors should be adjusted the same and draw the same amount of air. This can be determined with a "unisyn" or possibly a manometer. Another method is to listen to each carb intake with a hose up to your ear.

The book calls for inserting a piece of paper under each slow running adjustment speed screw, adjusting them until a slight resistance is felt removing the paper, then turning in the screw one turn. (this screw is to the left, and works against the throttle stop. Start with the center carb.

The idle mixture is controlled by the mixture control screw. It should be turned out one full turn to start. This screw is just to the right of the slow running screw. Turning it clockwise (in) leans the mixture. Tuning it out richens the mixture. (opposite of Amal motorcycle screws)

All other adjustments are made by changing jets. Since I didn't operate my car at high altitude, I never messed with the jetting. I am sure that Bill Watkins or some of the other race car drivers can guide you better in this regard. I go by the theory that if it isn't broke, don't fix it!!.

If you live in Denver, you will need leaner main jets and corresponding air bleed jets. As a rule of thumb, reduce the main jet by one size for each 3000 feet of altitude. It is important to make sure the engine is up to 70 degrees C before adjusting the carburetors. Also you need to be sure that all of your valves are seating properly and you don't have excessive wear in the valve guides.

From a whole lot of years of experience, I can deduce that if the engine is running poorly, the odds are that it is an ignition problem. While not ALWAYS true, it is the first place to start unless you KNOW that the problem is elsewhere.

Regards,

Jim McQuay
West Linn, Oregon
A/B 3015 and 3016
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[John Simmons]

The odd thing is: on page 8 of section 1, the ignition time is given as 23 degrees before TDC static advance. I've been unable to reconcile this with the 5 degrees given on page 80. Could the 5 degrees be for one of the lower tuned engines? Of course, since I don't have the Bristol engine in my car, I haven't had to resolve this myself.

[Rich Slevin]

Thank you for your offer to send any manuals you might have. Drivers, workshop, parts, whatever. I have none today and anything you care to send is appreciated. My email address is rich@odi.net.

Vin is 3066 and was owned by John Schieffelin in Mass. I bought the car 4 years ago and it has been at Mike Decola's shop being "restored" since. He is supposed to be one of the best guys on Bristol Engines. I just got the car moved out to my home in the SF Bay area last week. The car does not run well, has little power until it hits >3K RPM. A real flat spot in the lower end along with spitting and coughing. I checked the Dwell and it was 24 degrees, a bit low considering a 6 cylinder should be in the low 30's. Upon acceleration the dwell moved to over 30, but was inconsistent, clearly indicating either a point wear issue or distributor bushings. In checking the points, they are new, but I can physically move the distributor shaft and "adjust" the points from about -.016" to over 0.024". Point gap seemed too high even with the worn bushings, so I adjusted it down a bit to 0.012"- 0.016", and the engine ran better, but not well. I am thinking a quick resolution might be to put in a set of Pertronix point replacements that should not be affected by the bushings. The correct way would be have the bushing replaced, but that will take time. May do that later once I get the car running well enough and solve what I think might be a jetting problem. Any thoughts?

As for the timing. I am thinking I need to check both the dynamic timing at idle and at 3K RPM. Static always seems to be a few degrees off when set against dynamic, strobe timing. I read somewhere that at 3K RPM we should see 30 degrees. Not knowing the timing at idle, I cannot check that the distributor is allowing for the full advance curve. Any experience with this? Are there any specs out there on the AB engine?

Looking at the carburetors, do you know if the idle mix is the correct adjustment to make for lean low and mid end? Or is there an intermediate jet? I pulled the plugs out after taking a 10 mile drive at high speed. They all looked slightly lean, but reasonably consistent. Kind-of makes me think that either we have an ignition problem, or maybe some plugged low or intermediate jet, since the high speed seems consistent. I want to lock down the ignition issues first before I start tearing into the carbs.

Thanks again for your comments and support. Regards, Rich

[Rich Slevin]

Does anyone have a distributor advance curve for an AB? Latest effort was to change the springs in the Dist that was only getting 15 degrees advance. Now getting 30 degrees. Car runs better, but low end is still slow to pick up. I think the advance curve needs to come on sooner, but I have no specification as to the proper curve.

A few other things to sort out if anyone has any comments:

- Need to rebuild the carbs. The throttle shafts are a bit loose. Since the AB has no accelerator pumps, I think any air leakage may be contributing to the low end hesitation. Anyone know of a quality, experienced shop that does these?

- I have one of the rear torsion knuckles leaking gear oil through the boot. Do I need to pull it and rebuild? If so, where do I get parts for these? Any experience or comments are appreciated.

- I have an extra 4 speed transmission I would like to have rebuilt as a spare. Anyone know of a shop that has experience and access to correct parts?

Thanks for any support. -Rich

[Rich Slevin]

Solex's and distributor are now rebuilt and back in the car. Solex jets seem to be wrong as compared to the Arnolt book. Mine are 125 main, 190 air corrector and 47.5 pilot. Book says 135, 240 and 50 respectively. Anyone know which is correct at sea level? I have some jets coming that I need to drill out next week I though I would try a set of stock size.

Distributor was re-curved by Jeff Schlemmer who was recommended for Lucas distributors. I followed his recommendation and set the idle timing at 16 BTDC, but the low end was missing. He suggested resetting at 22BTDC, but my valves are rattling a bit. The distributor recurve seems to start advancing at about 2800 RPM and advances total of 24 degrees.

I am not sure if the carburation is the main issue or if is the distributor. But the bottom end has very poor acceleration until it gets to 2500 RPM of so. Anyone have any thoughts?

Thanks, Rich