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Exhaust heat riser modification ?
Posted: Sat Nov 05, 16 4:38 pm
by shaungriff
When I brought my cj at would barely run at low speeds due to the fuel boiling in the carb & tremendous intake heat (temp gauge ok) which was caused by the flap in the exhaust manifold being closed all the time forcing hot exhaust through the intake, I've fixed the flap into continuous open position & it now runs so much better. However if I get stuck in traffic & the temp gauge begins to climb a bit the idle starts becoming lumpy & I can see bubbles appearing in the fuel filter (on top of the intake) like the fuel is starting to vapourise, I've wrapped the fuel hoses in foil to try help. Is it best to fit a metal fuel filter or do you guys have any other cures ? Thanks shaun
Posted: Tue Nov 15, 16 4:04 pm
by Dave999
metal can away from the heat would be fine
but if it is touching the engine would be worse....
what is your ignition timing at idle?
what is the timing at 2500+
they run hot and slightly rich when they have too little initial timing.
how black is your tail pipe?
well they run hot for many reasons
low coolant
poor fan to radiator clearance
lost all the gunk in the viscous fan coupling
no shroud
stuck thermostat
blocked radiator
radiator cap seal poor
collapsing pipes
slipping belt
head gasket??
corroded pump vanes
erm any number of reasons
but try something easy first
but modern petrol burns slower and hotter than the old 4 star so they do need a little more initial advance than the workshop manual states in order to be happy
however don't add so much that you make total advance with the vacuum can disconnected more than 34*
if you can't add any more initial its time to think about a modified/recurved or different distributor with a shorter timing curve.
set it to 10 or 12 initial and go for a gentle drive see how you go
keep in mind that it will ping at higher RPM if the advance strays past a specific point north of 30 (usually around 34) over 3000 rpm so don't go there until you have checked total advance.
many will be running something like 10-15 initial and a total advance of 28-32
not 5* or 8* BTDC as the workshop book states
impossible with the standard distributor.
yours will potentially be a Bosch or Lucas distributor
I can tell you how to modify the Bosch one, you need to be bale to braze.
or swap it for a US 360 distributor and you can then buy an advance limiting kit to experiment with (none destructive modification using bolt on parts)
Dave
Posted: Thu Dec 01, 16 9:27 pm
by shaungriff
Hi Dave only just saw your reply. The timing it idle is 7 btdc so gonna try it at 10 & listen for pinking. Thanks shaun
Posted: Fri Dec 02, 16 9:30 am
by Charger
Posted: Sat Dec 03, 16 8:15 pm
by shaungriff
Thanks for replies, I'm experimenting with the timing thanks shaun
