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6 cyl Bristol cars Type 400 to Type 406

403 Carburation

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Old 10-03-17, 04:37 PM
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Default 403 Carburation

Finally got the car back but now need advice on carburation.

The triple Solex were (I assume) re jetted to 100B spec when the updated cam was fitted by Bristol and ran cleanly.

Following the rebore it now has Cosworth pistons of approximately 9.5:1 compression and the carburation is no longer clean, particularly at higher revs (3,000+ approx.).

Can anyone suggest what jetting I should use in the Solex carbs with 9.5:1 pistons?
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Old 10-03-17, 09:30 PM
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Peterg,
I suggest you check the sizes of the current jetting with jet drills as over 60 plus years owners often drill the jets larger.
The only accurate way to decide on jets required is to connect a gas analyser to the exhaust . I have found a mobile gas analyser on the road is better than
a rolling road dyno. When you know if it is running lean or rich at a particular rev range a decision to change jets can be made.

We might normally think that fitting higher compression pistons would require larger jets . This could be the case if the engine had previously been rejetted & adjusted/tuned accurately . But most Bristols with standard jetting run too rich , often a combination of high float level , worn jets over time and use of higher octane fuel than in the 50's.

Probably best to get an expert with a gas analyser and selection of solex jets to tune it and rejet as necessary. It could be cheap insurance for the money spend on a rebuilt engine.

Geoff
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Old 11-03-17, 01:08 AM
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Geoff/Peter
Burlen fuel services have just started to introduce fuel injection conversions for classic cars I don't know how feasible this would be for a 2 Litre Bristol but I seem to remember reading somewhere that this has already been done on a non commercial basis. I have just put an engine in my 401 which BCL told me was rebuilt by Eden Holder, the number one carb throttle body spindle or shaft was so badly worn on one end it would never have run properly.
The basic problem as I see it is that even rebuilding and re jetting original carbs may not give original performance and reproduction carbs are of variable quality.
Any thought on this option?
Geoff.
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Old 11-03-17, 04:24 PM
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Reading another forum about the Burlen system which at the moment covers some SU Carbs I saw mention of another company Classic Car Fuel Injection Conversion - Convert to Fuel Injection - Improved Starting, Running, Performance and Fuel Economy they actually list Bristol as one of the makes they can supply kits for but as they cater for american cars as well including Chrysler this may be for the later V8 cars.
I think if we do anything with my 403 later this year, head off awaiting repair at the moment, I might investigate this a bit further, not for the 401 as I had the parts to hand to replace the worn component.
Burlen can supply service parts for the carbs on a Bristol and I think still offer an overhaul service.
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Old 12-03-17, 05:19 AM
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Geoff K ,
Fuel injection to me is getting too far way from a Classic car of the 50's .

I have fitted quite a few new sets of Weber 34ICH carbs (with 27mm venturi) to various 6 cylinder Bristols (400,401,403,405,405DH ,406 &AC Aceca )
The first set took some sorting on my 400 . They idle so much better than a set of well sorted Solex . I don't think they produce more power but are easy to tune and parts are readily available.

Geoff D
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