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Cold Start Problems BN7

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Working on a friend's BN7 with H8(maybe HD8) carbs. When trying to cold start it will do a quick hit and die for a while then when it finally does start it spits and pops through the carbs. After it is warmed up, everything it smooth other than it hesitates when pulling off from a full stop. Owner says he uses the choke for the first few tries then takes it off to finally get it started.

Everything is currently at the stock settings, point type Lucas dizzy. When looking at the spark, to me, it looks pretty weak with the Lucas Sport coil. Looks like the vacuum advance is not working but I don't think that it the starting problem. Do not want to move to electronic, trying to keep this beauty as stock.

Any/all suggestions are appreciated.

BTW, I am TR3 guy just venturing into Healey-land for a friend.
 

mgtf328

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I had a similar problem. I found that the choke wasn't set up properly. If set correctly when you pull the choke out it squirts neat fuel into the carb body. What I do now is wait for the fuel pump to stop pumping , pull the choke in and out a couple times, wait a minute or two for it to evaporate and then start. Works like a charm.
I suspect though that your carbs may also need tuning, these cars like to run a little rich.

AJ
 

steveg

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If it's that hard to start, sounds like it's badly in need of a tuneup. The electrical stuff is more likely to be a problem than the fuel system.

Point gap, plugs, timing, carb float setting. Make sure none of the spark plug wires are loose.

Remove the domes and check the function of the choke and see if the jets return properly with the choke off. The jets should be down around .060" with choke off. 2" HD8s are non-standard, so check if it has the right needles (UH is standard) and they're set properly in the pistons.

When it's running, check for leaky butterfly shafts.
 
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Thank you mgtf328 & steveg,
This is a fairly fresh restoration, all electrical is new, and carbs rebuilt. Because of the weak spark I have ordered a new Lucas Sport coil. I will re-check the carbs as advised and check back. Many thanks!
 

vette

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Lean carbs.
 

Michael Oritt

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Assume nothing.
 

LarryK

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Pull plugs and check burn pattern, rich, lean, wet, dry. As above check choke. Pull carb tops check for oil, check diaphrams for holes. Once fuel, plugs are OK check timing and points. Just because points and condensor are new means nothing, check gap and grounding. Just a start. One thing at a time until you find it. Do too many at once, hides the problem.
 

Guffy60

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Plug gap.
Since I got poor cold start even though serviced and set up on rolling road.
I have re balanced carbs, as wasn’t done, redone timing was only at 6 degrees.
still no difference, took plugs out to do compression test, looked at gap, could drive and truck through it.
re gapped plugs and now starts first or second time, not first or twenty first.
 

LarryK

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Simple but will stop a lot. Good diagnostics.
 

BoyRacer

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Just to correct some things said earlier. The "choke" on an SU carburetor is nothing more that a forked lever that a pulls the jet down a bit, so that the gap between the jet and the needle is a bit larger, thereby allowing more fuel to pass creating a richer mixture upon start up. Secondly, there is no squirting of any fuel by pulling on the choke cable. And, as a reminder, there are no accelerator pumps in SU carbs, so pumping on the gas pedal will have no effect and pulling and pushing the choke in an out a few times will also have no effect.
 

Bob_Spidell

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... there is no squirting of any fuel by pulling on the choke cable ...

Probably not on H/HS carbs, but on HD carbs pressing down on the diaphragm probably displaces some fuel. Whether it goes out the jet openings or back into the float bowls or both, well, who knows. Guess I could try it on my BJ8, but that sounds like, you know, work ;)
 

mgtf328

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Well there must be something different about my BJ8 carbs then because they definitely squirt some fuel out if you pull the choke quickly.

AJ
 

LarryK

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Choke is only designed to enrich jets and close butterflies. Not like Holley, Motorcraft, Carter or Rochester that closes butterflies and has accelerator pump that squirts fuel into manifold.
 

red57

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I agree the choke is not designed to be an accelerator pump but, at least with HD's, it actually does squirt fuel when the jet is dropped quickly, the quicker you lower one, the bigger the squirt you get. I agree with Bob, the diaphragm displaces fuel when lowered and they will 'pump' a small amount of fuel.

If you have HDs you can see it for yourself if you remove the dashpot and piston so you can see the jet while quickly lowering it by raising the jet adjusting lever on the side of the carb by hand (wear glasses and don't get too close - don't want gas in our eyes).

All I have are HD type so I don't know if this phenomenon happens with H or HS type or not.

Dave
 
OP
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Hello All,
I think it was a bit of a multi-pronged issue. Choke cable was adjusted much too loose, so the HD8 was not giving any prime. The replacement coil provided a much stronger spark, and blue too!

A little oil in the dash pots and set the timing up to 15° and all feels good in the garage. Maybe a drive on Saturday, weather permitting.

One thing left; it appears the vacuum advance diaphragm is leaky, need to send off for a re-build.

Many thanks for everyone’s input!

Bill
 

steveg

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bob hughes

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And just before you set off on a marathon, just check the top/bottom plate on your dizzy to see if there is play vertically, my BJ7 would not start properly and tick over at 750 RPM until I replaced the three pronged star spring that holds the two plates together, my star spring had two points intact and the third was in the bottom of the dizzy. I do not know how it survived with the weights whizzing round.

:cheers:

Bob
 
OP
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And just before you set off on a marathon, just check the top/bottom plate on your dizzy to see if there is play vertically, my BJ7 would not start properly and tick over at 750 RPM until I replaced the three pronged star spring that holds the two plates together, my star spring had two points intact and the third was in the bottom of the dizzy. I do not know how it survived with the weights whizzing round.

:cheers:

Bob

Thanks for the tip, I went through the dizzy a few hundred miles back and all was OK. I’ll keep an eye on it.
 
OP
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If it's that hard to start, sounds like it's badly in need of a tuneup. The electrical stuff is more likely to be a problem than the fuel system.

Point gap, plugs, timing, carb float setting. Make sure none of the spark plug wires are loose.

Remove the domes and check the function of the choke and see if the jets return properly with the choke off. The jets should be down around .060" with choke off. 2" HD8s are non-standard, so check if it has the right needles (UH is standard) and they're set properly in the pistons.

When it's running, check for leaky butterfly shafts.

Been through all the tune-up steps, runs good/starts hard, I am thinking the issue lies in the choking linkage. I appears that even with all the cables adjusted there is not enough travel in the cable or knob to pull the HD8 levers in the their full upright position. Could this have anything to do with changing to the model HD8? As a TR guy, I am used to being able really pull the choke all the way and lock it with a quarter turn.
Thx, Bill
 

mgtf328

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I found that the choke lever, when in the fully open position (when the choke lever on the carb is as far down as it will go) has to turn some way before it has any effect on choke function. i.e. the first few degrees of the choke lever turn doesn't do anything. So when I positioned the cable in the choke lever clamp I pulled the choke lever up the cable until it was just below the point where I could see the choke started closing before I clamped it. That way you don't need to pull the cable out so far and when you pull the cable it opens the choke straight way. Worked for me.

AJ
 
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