From RON 98 to RON 95

[dnomyar]

Good day to all....
I noticed that when I switched gasoline from Phoenix RON98 which I have been using for the past 5 years to XCS RON 95 my vehicle's (Feroza 1600cc) idling increase from 800 rpm to 1,200 rpm without tweaking the carburetor. I thought it was just a timing adjustment so I let it be with the hope that my engine's rpm would normalize again. However after two weeks wherein I had to refill again with XCS fuel, the rpm is still high at 1,200 rpm. I tried to tweak the carburetor by adjusting the air and fuel ratio, but to no avail. With aircon on the rpm settles at 1,000 rpm when it used to be 800 rpm. Has anyone experienced this? Or perhaps I'll switch to Extra RON 93 later. I have to downgrade to RON95 because RON98 is no longer available here in our province in Quezon. TIA

[dr. d]

i don't daihatsu. but
a carb-ed engine should be easy to adjust for idling. there's the idling screw to turn.
and timing should be easy to check, if one has the requisite timing light.

is it possible, na nagkataon lang? that something else is wrong, and not fuel change?

do you have idle-up circuit? maybe may electrical connection na na-tanggal?

vacuum hose still in place and not leaking? vacuum diaphragm functioning and not stuck up?

but yes. these things tend to cause a drop in rpm and not increase...

[dnomyar]

i don't daihatsu. but
a carb-ed engine should be easy to adjust for idling. there's the idling screw to turn.
and timing should be easy to check, if one has the requisite timing light.

is it possible, na nagkataon lang? that something else is wrong, and not fuel change?

do you have idle-up circuit? maybe may electrical connection na na-tanggal?

vacuum hose still in place and not leaking? vacuum diaphragm functioning and not stuck up?

but yes. these things tend to cause a drop in rpm and not increase...

yesterday, i checked all vacuum hoses and found the two hoses attached to the idle up switch with cracked ends in it so I just cut the cracked portion and reattached the hoses. I was successful in lowering the idle rpm to 800. However, this morning, I run the vehicle for a road test and after it reached the operating temperature, the rpm is back at 1,200. I suspect that maybe it is now time to change the timing belt. My ride just turn 19 last Oct. 9 this year.

[dr. d]

yesterday, i checked all vacuum hoses and found the two hoses attached to the idle up switch with cracked ends in it so I just cut the cracked portion and reattached the hoses. I was successful in lowering the idle rpm to 800. However, this morning, I run the vehicle for a road test and after it reached the operating temperature, the rpm is back at 1,200. I suspect that maybe it is now time to change the timing belt. My ride just turn 19 last Oct. 9 this year.

maybe you should consider replacing the entire lengths of the vacuum hose? it's cheaper and easier than replacing any belt.

cold engine.. 800 rpm.. idle-up circuit.. operating temp.. 1200 rpm...
i am sure there is a unifying equation somewhere here, but i can't quite get my finger on it.

i do not think it's the timing belt.
"hey! mahal ang timing belt."

[dnomyar]

maybe you should consider replacing the entire lengths of the vacuum hose? it's cheaper and easier than replacing any belt.

cold engine.. 800 rpm.. idle-up circuit.. operating temp.. 1200 rpm...
i am sure there is a unifying equation somewhere here, but i can't quite get my finger on it.

i do not think it's the timing belt.
"hey! mahal ang timing belt."

I couldn't agree more.. I'll bring it to my trusted repair shop for diagnosis but first I'll try to replace the old hoses with new ones. thank you for the suggestions... with fingers crossed.

[Lew_Alcindor]

I hope you did not mess with the A/F ratio. As mentioned, there is a screw for idling which is different from the A/F screw.

If I am correct, there are some carburetors which allows for higher RPM during cold start then gradually lowers RPM as the engine gets warm. So that maybe your case.

But if you are not sure, have your carb cleaned or overhauled. Carb is a PITA for DIY.

[Lin Dan]

I had an '89 Feroza and the carb reacts instantly to the type of gasoline you would put into it. I suggest at least RON 95.

[SoleusBB]

If I am correct, there are some carburetors which allows for higher RPM during cold start then gradually lowers RPM as the engine gets warm. So that maybe your case.

Yes. It's called automatic choke, contrasted dun sa mga 70's era "junk cars" I used to drive that had a manual choke knob you pulled out during cold starts, then pushed back in when warmed up na.

The onboard CPU in new cars do this also.

[dnomyar]

I hope you did not mess with the A/F ratio. As mentioned, there is a screw for idling which is different from the A/F screw.

If I am correct, there are some carburetors which allows for higher RPM during cold start then gradually lowers RPM as the engine gets warm. So that maybe your case.

But if you are not sure, have your carb cleaned or overhauled. Carb is a PITA for DIY.

There are two screws at the face of the carb which I adjusted counterclockwise then clockwise. Parang trial and error lang ginawa ko until it reached the desired rpm of 800. the problem is the next day when I test drive the vehicle until it reached its operating temperature, the rpm was back at 1,200. is there other screw for the A/F ratio?

[dnomyar]

I had an '89 Feroza and the carb reacts instantly to the type of gasoline you would put into it. I suggest at least RON 95.

but the manual indicates RON90 or higher. though ever since I am using RON95; shift to Blaze 100 then when I settled down in our province then downgraded to Phoenix RON98 due to inavailability of Blaze100, then after 5 years back to XCS RON95.