Poor MPG

[I'm_a_Newbie]

OK, so yesterday I finally found time to check the front cylinder valve timing to see if this was causing the poor MPG on my SV. Found the timing to be spot on. (Had front head off beginning of Summer).

I did notice though that the clear poly pipe I connected to the rear vacuum nipple was discoloured. Perhaps this is a sign that the valves are not sealing properly. I am going to check the valve clearances today in case they have closed up on the rear. This could also explain why the vacuum balances were way off after the rebuild.

If the clearances are OK then all I can do is recheck the vacuum balance and TPS adjustment.

[Viney]

What to you class as poor mpg?

[G]

How you ride effects the mpg massively.

If I'm out having a play or even cruising at 80- 90 on the motorway I can get 100 miles to a tank = crap mpg.

If i'm doing long distance I cruise at 65-70 very light on the throttle and have got 160 miles to the tank without seeing a petrol light and it worked out at over 60mpg.

I think perhaps you are looking into it way to deeply?

[John 675]

although i have a big dent in my tank, i normally get 130 to the tank,
then i started using redex injector cleaner, now my petrol light comes on at 130 miles.. i know its not a coinsidence because i always ride roughly the same way,and its been consistant over the last four tanks.. dirty carbs/injectors? cant hurt to try :D

[Jase22]

Does your bike run really rough? Could be a valve that's not seated correct causing poor mpg, this wouldn't be detected when checking clearances.

[yorkie_chris]

Compression test would tell you this quicker.

[I'm_a_Newbie]

Ok, here is an update after today's work.

Front valve timing spot on
Rear valve timing spot on
Front and rear inlet valve clearances all 0.10mm
Front and rear exhaust valve clearances all 0.20mm
Throttle sync slightly off (not like last time), adjusted
TPS adjustment spot on
STV Sync spot on

Fitted 2 new NGK CR9EK plugs today. Since the rebuild I had 1 Denso and 1 NGK.

I do have a compression tester but not with the correct adaptor for the SV plugs size. The front valves are sealing correctly as when I had the head off I did a leak test using paraffin. If there is a problem it would be with the rear valves.

The bike is running very smooth and seems to have full power. I am only getting 90 miles to the fuel light when I was getting 120 before the front head came off. The end of the exhaust (standard) keeps getting covered in soot as if it is running to rich.

Tomorrow I am going to get a new air filter element as the current one is a bit dirty.


Anybody near Portsmouth got a compression tester?

Tim

[Yellow SV]

Sounds poor, I have managed about 200 before havimg to fill up but that only equates to high 50s (I think gentle running should give over 60). As you are using the light as the measure (or are you actually calculating amount used) is it possible that while the tank was off to do the head that something has happened to the sender to give a "false" reading?

[I'm_a_Newbie]

Sounds poor, I have managed about 200 before havimg to fill up but that only equates to high 50s (I think gentle running should give over 60). As you are using the light as the measure (or are you actually calculating amount used) is it possible that while the tank was off to do the head that something has happened to the sender to give a "false" reading?

Yes it always takes the same amount of fuel. Infact on the last fill as soon as the light came on I managed to get almost £13 worth in, it's always floated around the £12 mark.

Ran it over to Bursledon today and picked up a new air filter. It is running really smooth, the best ever. If I can get a compression test on it the only thing left is a Dyno and ECU re-map.

Tim

[ASM-Forever]

Damn those increased petrol prices. :)

[Yellow SV]

Mine is a curvy, hence carbs but light usually comes on at circa 145 to 160. Average over the years has been 55 mpg with a best of 60. Your £13, using the above calc, equates to 48 to 53 which is poor but not disastrous. If you can get significantly better I too would like to know how it's done as I feel the bike should be much better when used in a steady manner (65 from a ZZR 1100 by a pal when on the way to the Island).

[John 675]

black soot?, might want to check your oil with that one as well mate, seems obvious i know but often overlooked untill it seizes,
is it FI or carbed? :)

[I'm_a_Newbie]

Mine is a curvy, hence carbs but light usually comes on at circa 145 to 160. Average over the years has been 55 mpg with a best of 60. Your £13, using the above calc, equates to 48 to 53 which is poor but not disastrous. If you can get significantly better I too would like to know how it's done as I feel the bike should be much better when used in a steady manner (65 from a ZZR 1100 by a pal when on the way to the Island).

At £12.80 @ 95 pence per litre it works out to 3 gallons, over 90 miles this is only 30 mpg

Where did u get 48 to 53 from?

[I'm_a_Newbie]

black soot?, might want to check your oil with that one as well mate, seems obvious i know but often overlooked untill it seizes,
is it FI or carbed? :)

No worries as far as oil is concerned. I check it regularly. It has never needed topping up and I change the oil and filter every 4500 miles.

Tim.