Cold Start Device

[John Reay]

Is it commonplace for the cold start device to fail on DCOE's?

 

Is the cure to remove the choke thingy or do I have to block up the cold start holes in the venturi?

 

Thanks

 

JOhn

[Mr Locust]

How exactly has it failed?

[John Reay]

Car has been running fine but now it is fouling plugs 1 and 2. I can screw the idle mixture screws in and it improves the idle.

 

Needle valves have recently been changed and fuel pressure is 2.5psi.

 

%CO level is horrendous, HC levels are dire as well, so I am hedging my bets on the cold start device.

 

John

[Graham Sewell]

Start with the basics - check the carb balance as this has much the same effect on the plugs. If you have the standard Caterham setup, the cold start device is never used (i.e. no cable attached to them). In either case, push the levers forward to shut them off (they are normally sprung that way anyway).

 

Then set the idle speed and tune the idle mixture screws as per the build manual (max revs for a throttle setting at idle speed) and then probably close down by 1/4 turn.

 

Also air check for leaks around the carb/manifold and manifold/head joins - spray with WD40 and the engine speed should stay the same. If it increases, you've got a leak.

[Mr Locust]

You say that the needle valves were changed recently.

 

Have you checked for debris in the needle valve on front carb?

 

i.e. is it not shutting off fuel supply at the correct level and causing massive overfuel problem?

[John Reay]

There is definately a fuelling problem. Balance is okay on the carbs. Idle jets are 45F9's for a 1600xflow.

One day the car is fine, the next I have serious exhaust popping and nanging because of unburnt fuel. HC levels and CO levels are huge.

 

It is either the floats sticking, needle valves not shutting or the starter valves have got jammed open.

If I screw the idle mixture screws right in the idle speed improves, so fuel is getting in from somewhere. On the other carb, screwing the idle screw in or out does what you expect it to do ie idle speed suffers.

 

Ho hum, off with the carbs this weekend

 

John

[Mr Locust]

I had a similar problem with poor idle etc on Triumph 4 cyl engine fitted with 2x 40dhla dellortos.

 

Are the spring washers on the mounting plates broken or overtightened?

 

If the carbs are locked solid the idle characteristics can be v. unpredictable & impossible to set up for smoothe idle.

 

If the problem is at idle, look to see if a noticeable 'shake' seems to set in on the carb(s) when the problem starts.

 

I found that rubber isolating bobbins from aldon auto were crap and that zinc plated thackery washers were brittle - black finish thackery washers seem to work fine.

[John Reay]

biggrin.gif biggrin.gif

 

Just to let you know looks like it was the starter valves jamming slightly open giving excessive fuel at idle. Blocked the passages up, removed the choke levers, fitted blanking plates.

 

Refitted the Webers, balanced and set idle. CO and HC reading are now back to what they should be.

 

Happy days

 

JOhn