Mark and Judy Dalmaijer wrote:
>
> Hello All
>
> I have a TR4 I bought last summer which started OK (but not great) last year
> and then this year has been starting poorly. It would take a lot of
> cranking, pulling out the choke, pushing it in, flooring the gas and then no
> throttle and FINALLY it would start. Once warm the engine started fine.
>
> I just recently put in new stock air filters, plugs, condensor and points,
> cleaned the fuel screen and bowl of all sediment and tried centralizing the
> jets according the Bentley manual. I also removed the air pistons and
> cleaned them up as well as the bores.
>
> Now it isn't starting at all and will after a lot of cranking cough and come
> close to starting and die. When I pull the plugs they don't seem to smell
> too strongly of gas as I assumed they would with all the choking. What is
> the best method to measure how well the fuel pump is working? Measure a
> volume/minute or pressure? Also, I pulled 2 plugs and cranked the engine
> over and the spark seems to be very weak. Do coils "go" over time? How do I
> measure current coming from the coil to the distributor.
>
> The Bentley manual is fantastic but unfortunately I am a "wanna-be" mechanic
> and need some help in problem solving which this manual doesn't really do. I
> would appreciate any helpful advise which would let me enjoy my car for the
> short summer that we get here in Alberta, Canada.
>
> Thanks in advance for your help!!!
>
> Mark Dalmaijer
The "air pistons" are the heart of the SU carbs you have on your TR.
They actually operate under vacuum. As the vacuum in the manifold of
your car varies, so does the position of the piston in the dashpot. This
varies the position of the tapered needle in the jet, thus varying the
mixture. The important thing to remember is that the small cylinder on
top of the large pistons MUST be filled with oil. The coil spring inside
the dashpot and this cylinder/piston (when filled with oil) constitute a
damped system and stops the needle "fluttering" in the jet. Without the
oil, the piston will move up and down rapidly under the influence of
vacuum, rather than the smooth movement that is optimum. You should not
that the large piston has a very small clearance in the dashpot bore - if
your "cleaning" resulted in the removal of any metal from either the
piston OD or the dashpot ID, you will have increased the clearance and
possibly reduced the carbs ability to meter fuel correctly.
The second thing to look at is the choke linkage. The choke is actually
an enrichment device that operates by pulling the jets down from the body
of the carb. This has the effect of moving the needle relative to the
jet, thus providing a richer mixture. The amount of movement is about a
quarter inch, I think. Also, when the choke is pulled out, the throttle
should open slightly. Your Bentley manual describes how to check and
adjust this.
Good Luck!
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