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BJ8 + Novice. Idle speed adjustment help req'd.

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RobWarren

Jedi Hopeful
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Wise Gentlemen,

I've scoured through the different topics regarding idle speed but I have a couple of problems that might be related and would like to get your ideas.

First problem: Idle speed is too low. Occasionally stalls when warm so I think I need to just take it up to around 800 (is currently at 500).

Second problem: First the back one and now both suction chamber caps are coming off during a drive. Rear one has a thread which I can't tighten very much as it's damaged (must have been overtightened), front one can be tightened a great deal but still works it's way off. Both are plastic and original.

Should I be messing around with idle speed before I've figured out why the caps are coming off? Engine head was recently tightened and tappets adjusted after an engine rebuild and 500 mile run-in. I'm not sure if the mechanic who did it has done something wrong as the previous owner said it had never happened to him (and he's an honest bloke, I trust him implicitly).

Finally, to increase the idle speed - what is the correct procedure and does anyone have a photo of which screws need adjusting? My workshop manual AND driver's handbook have been "borrowed"!

Thank you all in advance

Bob
 
Re: BJ8 + Novice. Idle speed adjustment help req'd

Hi Bob,
I think you can go here & find all of your HD8 information.
https://www.hazelden.ca/austinhealey/index.html

I would get a couple of new caps/dampers. If the threads get worn it's impossible to keep them tight. I might also put a couple of wraps of Teflon tape around the new threads.

The most common reason for the caps to be "blown" off is a pop back through the carbs as happens on lean or cold acceleration. This problem will be greatly increased by too lean mixture settings. Try to stay on the rich side of the mixture settings. Sometimes the BJ8's require a bit of choke for a quite a long time during warm up.

The damper is a one way hydraulic valve that should present quite a bit of resistance to the side upon it's opening but no resistance to closing. Thus the blowing out/cap stripping if a back fire puts a lot of opening force on the slide.

Note on these particular carbs that idle speed is set by a separate adjusting screw & not by the throttle blade position. I think the reference will explain it. Note 9 on page 4.
D
 
Re: BJ8 + Novice. Idle speed adjustment help req'd

Hi Bob, I think the HD8 Carbs are some of the simplest SU's to set up because all the adjustments are done by screws that are readily accessible. You should separate the carbs first before attempting an adjustment and set them both up the same for initial tuning. Firstly, the throttle shafts are to be closed to adjust the carbs and they will stay closed at idle. The idle adjustment screw is the largest of all the screws seen on the carb when looking straight downward with your head over the carbs. it is located to the right of the main body of the carb. With the throttle plate closed, this screw regulates the passage of air/fuel mixture around the throttle plates thereby giving the engine enough mixture to idle on. Set them each at about 2 1/4 to 2 1/2 turns out from bottom. You'll notice i said this regulates mixture. That means it is allowing to pass the mixture which is set by the main jet adjustment. If the jet is adjusted rich, the idle mixture will be rich. If the jet is adjusted lean, the idle mixture will be lean. So you must set the jet adjusting screw correspondingly to get a good mixture. It is the small screw with the head facing up on the opposite side the the main body of the carb from the idle screw. If you look closely you will see that it is connected to a lever which is moving the jet by motion of a diaphram. I'm sorry I don't have the initial setting of this jet adjusting screw off the top of my head. But this is the process where you lift the piston and if the engine stalls the jet is too lean and if the engine speeds up and seems to run on the jet is too rich. Anyway, get the mixture adjusted right then fine tune the idle speed. A couple of things to remember, when it comes to idle speed, set both adjusting screws on both carbs the same. Also if the jets are adjusted lean, richening them alittle will speed up the idle to a point. Also, make sure the spark plugs are real clean. Get new ones if you have to.
Hope this helps.
 
Re: BJ8 + Novice. Idle speed adjustment help req'd

When I lived in Rhode Island several years ago when I was in the Navy I had my carbs adjusted by a guy who did them in such a way that I could actually see the "rise" in the engine rpm as shown in the manuals for correctly adjusted carbs. I have not heard or seen his way of adjusting SU's since then.

If anyone would like to know how this was done please reply to this email as it's a long but factual procedure, etc.
Patrick
 
Re: BJ8 + Novice. Idle speed adjustment help read.

rob, i had the same problem when i first got my bj7, after much adjusting i found that who ever rebuild my carbs had used one wrong "cap damper" assembly ( rear carb), it had gotten so bad i had to safety wire it to keep it down, turns out it was from a triumph, after personally rebuilding both hs-6"s with the correct parts it was night and day, i.m.o. these carbs are a wonderful design and simple to rebuild. /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif
 
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