What could be wrong? It is hard to start even with the choke and until it is warm it would not accelerate especially at part throttle it is like it is running out of fuel but it would idle fine
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| Hesitation at part throttle https://ausmini.com/forums/viewtopic.php?f=2&t=99423 |
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| Author: | GuamMini [ Tue Oct 22, 2019 2:15 pm ] |
| Post subject: | Hesitation at part throttle |
What could be wrong? It is hard to start even with the choke and until it is warm it would not accelerate especially at part throttle it is like it is running out of fuel but it would idle fine
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| Author: | gtogreen1969 [ Tue Oct 22, 2019 3:09 pm ] |
| Post subject: | Re: Hesitation at part throttle |
First thing to check is the damper oil in the SU's |
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| Author: | GuamMini [ Tue Oct 22, 2019 3:55 pm ] |
| Post subject: | Re: Hesitation at part throttle |
Is the oil too thick or too thin? logic is the damper does not go up as fast as the butterflies open thus leaning out the mixture is that a correct assumption? |
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| Author: | gtogreen1969 [ Tue Oct 22, 2019 4:04 pm ] |
| Post subject: | Re: Hesitation at part throttle |
GuamMini wrote: Is the oil too thick or too thin? logic is the damper does not go up as fast as the butterflies open thus leaning out the mixture is that a correct assumption? Thicker oil gives a slower piston lift and richer mix / greater "accelerator pump" effect.Thinner oil or a low level allows the piston to lift quicker giving a leaner mix. Many acceleration issues I see are because there is low oil in the damper and the engine is starving on acceleration. |
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| Author: | GuamMini [ Tue Oct 22, 2019 4:39 pm ] |
| Post subject: | Re: Hesitation at part throttle |
gtogreen1969 wrote: GuamMini wrote: Is the oil too thick or too thin? logic is the damper does not go up as fast as the butterflies open thus leaning out the mixture is that a correct assumption? Thicker oil gives a slower piston lift and richer mix / greater "accelerator pump" effect.Thinner oil or a low level allows the piston to lift quicker giving a leaner mix. Many acceleration issues I see are because there is low oil in the damper and the engine is starving on acceleration. hahaha my assumption is the opposite thanks I will give this a try |
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| Author: | phillb [ Tue Oct 22, 2019 7:45 pm ] |
| Post subject: | Re: Hesitation at part throttle |
GuamMini wrote: gtogreen1969 wrote: GuamMini wrote: Is the oil too thick or too thin? logic is the damper does not go up as fast as the butterflies open thus leaning out the mixture is that a correct assumption? Thicker oil gives a slower piston lift and richer mix / greater "accelerator pump" effect.Thinner oil or a low level allows the piston to lift quicker giving a leaner mix. Many acceleration issues I see are because there is low oil in the damper and the engine is starving on acceleration. hahaha my assumption is the opposite thanks I will give this a try Yes it’s the opposite to what seems logical. The delay to piston lift = temporary smaller air opening = higher air velocity = a burst of fuel. Sent from my iPhone using Tapatalk |
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| Author: | GuamMini [ Tue Jan 28, 2020 11:26 am ] |
| Post subject: | Re: Hesitation at part throttle |
now it will not start. I am checking on the ignition timing and system |
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| Author: | 1071 S [ Thu Jan 30, 2020 3:50 pm ] |
| Post subject: | Re: Hesitation at part throttle |
I’ve said it before ... SU damper oil viscosity doesn’t really do much of anything .... SU used the same oil for the 32 hp 850s as they did in 75hp 1275s ... I would suggest using any engine oil you have on hand. Its a damper, much as the suspension shock absorbers. It stops the system bouncing around but any effect on the speed of movement will be pretty hard to detect. If you actually watch the piston move if you snap the throttle open, it will basically move faster then the eye can follow. IME, if you don’t use any oil at all, the engine will be a pain to start but on the move it will be hard to detect any problem... As they say, 90% of SU problems are electrical ... think about it. If it ran OK before the first thing I’d do would be to check the timing ..and then see if I could borrow a known good coil and try that. Cheers, Ian |
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| Author: | TK [ Thu Jan 30, 2020 6:06 pm ] |
| Post subject: | Re: Hesitation at part throttle |
"Thicker oil gives a slower piston lift and richer mix / greater "accelerator pump" effect. Thinner oil or a low level allows the piston to lift quicker giving a leaner mix." How? I would have thought when the piston rises it lets in the same amount of fuel and air regardless of how thick the oil is. The piston regulates the fuel and air. |
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| Author: | gtogreen1969 [ Thu Jan 30, 2020 11:45 pm ] |
| Post subject: | Re: Hesitation at part throttle |
TK wrote: "Thicker oil gives a slower piston lift and richer mix / greater "accelerator pump" effect. Thinner oil or a low level allows the piston to lift quicker giving a leaner mix." How? I would have thought when the piston rises it lets in the same amount of fuel and air regardless of how thick the oil is. The piston regulates the fuel and air. A slow piston to rise will temporarily increasing the speed of air through the venturi when the throttle is suddenly opened. Increasing speed through a venturi will lower the pressure of the air creating a sucking effect. It will increase richness of the mixture by sucking more fuel than it would if the piston was fully raised and the venturi fully open. Most of the issues I have seen are not with the weight of the damper oil but the lack of enough oil. Unless your a mechanic superstar who can feel the difference between 20w and 30w or summer and winter. |
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| Author: | drmini in aust [ Fri Jan 31, 2020 3:40 am ] |
| Post subject: | Re: Hesitation at part throttle |
Is it stock? If it has a sports filter it needs a richer needle. |
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