car revs after lifting throttle, only under load

[egres_svk]

hi again,

i am sorry that my thread is again about problems, but problems are to be sorted

when i start engine and rev it, it goes back to idle fine.
when it has proper temperature and i do whatever i want with throttle on neutral or clutch, goes back to idle fine


when the engine is heated properly and i drive say 50 kph on 4, 2000rpm, engine under medium load.. i then lift throttle and press clutch.. engine revs up to 3000rpm for a few seconds, then returns to idle.. higher load, longer time

when the needle just leaves L mark on temp meter, it revs too, but only a little

when there is no load, e.g i rev it on neutral, no problems..

is it autochoke? i remember, last time i checked the butterfly, it was in one position, i touched it with my finger and it opened fully.. then i could move it freely as i wanted, not much resistance at all.. vacuum valve controlling flap is ok..

engine starts ok when hot and also cold (20 deg C)

it did this to me once, after i was messing with carb, replacing hoses, cleaning it.. then after 2 weeks it stopped when i was messing with carb again.. now it of course started after i cleaned the carb from the inside and outside etc

i read about autochoke in these forums, but problems were connected with starting when hot - not my problem.. also found guide from one of the members about checking the flap when cold, then watching it open.. did not have time to do that yet, will do tomorrow or this evening

thanks a lot

 

[egres_svk]

anybody?

 

[imp124]

is the second vaccum operated barrel in the carb working properly, (this opens at 3,300 - 3,500 rpm approx i think?

cheers

Steve

 

[Ed]

That could be what it is. A 1.2K10 I drove with ECC did exactly the same thing. Was really annoying.

 

[egres_svk]

how do i find out what is wrong with second barrel? you said it is vacuum operated - i have vacuum gauge permanently connected. .do you know when it opens?

can i simply disconnect and plug one of the vacuum hoses controlling 2nd valve to stop it? which one is it?


btw.. when you said it is vacuum operated 2nd valve.. i got an idea.. more exactly a confirmation..

my vacuum gauge shows everything as usual.. it is connected to the line which also feeds vacuum advance..

when the carb did not rev like this, as soon as i lifted foot from the pedal, vacuum went to 22-26 inHg.. and also the car started to slow down..

now when the carb revs, when i lift the pedal, it shows 22-26 inHg.. no delay, exactly like before.. it means that the throttle cable is not sticking.. because primary chamber is closed, there is high vacuum.. so the engine must be fed from secondary chamber.. it confirms the theory..

(if i connected vacuum gauge to another hose, would i see 2nd chamber vacuum, or something showing me operation of 2nd chamber?)

 

[imp124]

i would just take the carb off and give it a good going over, cleaning etc... when mine was stuck closed i pushed the lever with the rod on the end in and out a few times with some WD40 on and it works ok now

steve

 

[egres_svk]

made some progress and found out few things...

i've called my friend today and we had a look at it.. on a parking place i got into the car, got the 1st gear in while standing on brake.. then i stepped on throttle and also started to release clutch.. (whole point is to get the engine into load while not moving)

my friend reported (looking at the main rod operated by the throttle cable):

when engine was idling and i slammed the throttle, rod turned and quickly returned back

when i got the engine under load and then released everything, revs jumped to 3000rpm as usual and he DID NOT feel fast coming back.. the rod slowly returned to idle position..


we have also found another lever on the other side of carb.. under the window with fuel.. looked like this opens secondary chamber, after pushing it, the engine revved.. when we did our load test, this did not moved..

however, because primary flap rod looks like it is sticking under load, i do not suspect secondary chamber anymore.. tomorrow i'll try to clean it again and maybe fit stronger return spring.. just to try.. because we repeated the load test and as soon as i released everything, my friend pulled the rod//throttle thingie back and engine stopped revving immediatelly

what do you think?


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btw for the future: shall i take some photos and add them to my posts for you to get into it faster? if i post a pic with red arrow, it should be better than saying "throttle rod/thingie"